KR20100112956A - Pattern of the front electrode of solar cell and solar cell using the same - Google Patents

Abstract

PURPOSE: A front side pattern electrode structure of a solar cell and a solar cell thereof are provided to prevent the decrease of the fill factor of a solar cell due to disconnection by connecting a finger line which is formed in the front side of the solar cell. CONSTITUTION: A front side pattern electrode is located on a silicon substrate. A finger line(110) forms the front side pattern electrode. An auxiliary finger line(120) interlinks the finger line. The auxiliary finger line forms at least one finger line cell which interlinks the separated space of an adjacent finger line. A bus bar(130) electrically connects each finger line to each other.

Description

Structure of front cell of solar cell and solar cell using same {Pattern of the front electrode of solar cell and Solar cell using the same}

The present invention relates to a solar cell, and in particular, by connecting a part or all of the finger line formed on the front of the solar cell, when the finger line is disconnected, electrons can be collected by the bus electrode, which is effective by the electrode disconnection. Significantly reduces the photovoltaic area, prevents the reduction of the fill factor of the solar cell due to disconnection, and minimizes the reduction of photoelectric conversion efficiency due to the disconnection. It is about.

Solar cells convert the energy of sunlight into electrical energy. This solar cell has a different structure from the chemical cells so far, and can be called a “physical cell”. The solar cell generates electricity by using two types of semiconductors, a P-type semiconductor and an N-type semiconductor. More specifically, when light shines on a solar cell, electrons and holes are generated inside. The generated charges move to the P and N poles, and a potential difference (photovoltaic power) is generated between the P pole and the N pole by this phenomenon. At this time, when a load is connected to the solar cell, a current is applied to the photovoltaic effect.

Solar cells can be roughly divided into those using a silicon semiconductor as a material and a compound semiconductor as a material. Again, silicon semiconductors are classified into crystalline and amorphous systems. This is even more diverse, including what is currently under development. Regarding the technology development of solar cells, improvement of conversion efficiency, price adjustment, etc. are planned. The company is also developing solar cells that exceed 20% conversion efficiency and thin film solar cells that can lower prices. At present, silicon semiconductors are mostly used in photovoltaic power generation systems. In particular, single crystal and polycrystalline solar cells of crystalline silicon semiconductors are widely used because of their high conversion efficiency and high reliability.

The most widely used type of solar cell for commercial use is a crystalline silicon solar cell using a silicon wafer, which currently exhibits the highest commercialization efficiency of 15% or more. The manufacturing method for forming the electrode of such a crystalline silicon solar cell is known a number of methods, the method of forming the electrode by screen printing is most widely known in commercial.

The general structure of the solar cell will be described with reference to FIG. 1A.

The solar cell forms a P-N junction on the silicon (Si) wafer substrate 10 to form an upper N layer 20 on the substrate and a lower P layer 30 on the substrate. The front electrode 40 and the anti-reflection film are formed on the upper surface of the N layer 20, and the rear electrode 60 is formed on the lower surface of the P layer 50 using Al (aluminum paste). In addition, the tab electrode 70 for soldering the tabs that electrically connect the solar cells to each other in the solar cell module is formed by screen printing, and is heat-treated at 900 to 1000 ° C. for completion. When light shines on a solar cell formed with such a structure, electrons and holes are generated therein, and charges formed as shown in the figure move to P and N poles, and a potential difference is generated between P and N poles by this phenomenon. Connecting a load to the solar cell causes the current to flow. That is, among the generated charges, electrons move toward the N-type semiconductor 20, holes move toward the P-type semiconductor 30, and each charge moves to the bonded electrode so that a current flows.

Among these, the aluminum paste used for forming the electrode diffuses Group III aluminum (Al) into the silicon wafer (Si) during heat treatment to form a back surface field (BSF), which is a P + layer, and electrically contacts the silicon wafer. Done.

Currently, researches related to solar cells are focused on lowering the manufacturing cost of solar cells and improving light conversion efficiency. In order to improve the conversion efficiency of the solar cell, it is necessary to increase the reflectance of the solar cell to sunlight, reduce the coupling degree of carriers, and lower the resistance of the semiconductor substrate and the electrode.

To this end, the Republic of Korea Patent Publication No. 10-2008-92583 has attempted to increase the conversion efficiency of the single crystal silicon solar cell by improving the structure of the silicon substrate and the front electrode to lower the transfer resistance of the carrier.

To this end, as shown in FIG. 1B, the finger line 40 pattern of the front electrode formed on the single crystal silicon substrate 10 is formed to be perpendicular or parallel to the silicon crystal direction, thereby causing side resistance ( The lower the lateral series resistance, the better the fill factor. Reference numeral 10 corresponds to the bus electrode.

However, the solar cell proposed by this conventional technology is applicable only to a single crystal solar cell. Currently, cell makers (Cell maker) of most domestic and foreign solar cells use polycrystalline wafers, and this technology cannot be effectively applied. . Furthermore, the formation of electrodes perpendicular to or parallel to the crystalline direction of the single crystal may facilitate the movement of electrons, thereby contributing to the improvement of the fill factor. However, if the front electrode becomes disconnected in the process of printing and firing, the decrease of the fill factor is rather reduced. This causes a problem in that the photoelectric conversion efficiency is reduced.

In addition, efforts to prevent the reduction of the light receiving area of the solar cell due to the miniaturization of the front finger line pattern have been attempted with other efforts. In other words, due to the formation of the front finger pattern, it covers 4 to 5% of the total solar cell light receiving area, which affects the characteristics of the solar cell fill factor.

Therefore, solar cell manufacturers can reduce the front electrode line width to improve the aspect ratio of the structure of the solar cell front electrode and minimize the covering area of the light receiving area while improving the front electrode thickness to improve the series resistance characteristics. The implementation of the width is trying to reduce the impact that can be broken. In the past, the line width of the front electrode was mostly implemented at about 110 μm. Currently, most of the front electrode is implemented at 90 to 100 μm.

However, the reduction of the electrode line width improves the disconnection failure rate, and when the disconnection of the front electrode pattern occurs, the generated electrons of the portion are not collected and disappeared, which causes a fatal problem leading to a decrease in the fill factor and the photoelectric conversion efficiency. It happens.

In an attempt to overcome this problem, some manufacturers have tried to improve the height at a thin line width by printing the front electrode pattern several times in succession.

That is, as shown in FIG. 1C, as shown in (a), as shown in (b), as compared to the general finger line printing method in which the thickness of the finger line 40 on the wafer 10 is 120 to 140 mu m. In the structure in which the finger lines are printed on the wafer 10 in the triple stacked structures 40a, 40b, and 40c, the line width is narrowed to 60 to 70 mu m and the height is increased. (c) shows an SEM image of a fingerline having a thickness of 60 μm and a height of 60 μm implemented through 10 laminated printings. The table shown in (d) compares the thickness and height of the fingerline implemented through the general standard type, the 3 stack printing, and the 5 stack printing, respectively. It can be seen that the effect of increasing the height is realized, so that a high aspect ratio characteristic can be realized, and that the resistance of the series resistance can be improved due to the reduction of the surface resistance according to the increase of the height (thickness). .

This multi-layer printing method causes an increase in the tact time of the process by repeating the printing and semi-drying steps, thereby causing a problem of deterioration of the cell's per-hour production capacity. do. In particular, it is difficult to align between layers according to the repeated printing method, and recently, it has been found that the defective rate of the array reaches 40% in the method of adopting such a method. Furthermore, such a stacked type method also cannot be free from the problem of the reduction of the fill factor of the solar cell and the reduction of the photoelectric conversion efficiency due to the loss of electric charge due to disconnection.

In this regard, there has been an attempt to form a pattern of the front electrode in order to increase the photoelectric conversion efficiency, which will be described below with reference to the invention described in Korean Patent No. 10-0652103.

Referring to FIG. 1E, (a) illustrates a front electrode of a solar cell, which forms a plurality of grid electrodes 46 orthogonal to the main electrode 47 on a silicon substrate 41 and adjacent grid electrodes. The distance between the electrodes is shorter than the width of the main electrode, and electrical connection between the grid electrodes is performed by the main electrode 47. In addition, the width of the grid electrode is narrow and thick, and the grid electrode is connected through the main electrode to reduce the area of the electrode without increasing the series resistance of the surface electrode, thereby improving the conversion efficiency of the solar cell.

However, in the structure of the pattern electrode of this type, as shown in (b), both ends of the grid electrodes are formed in an open shape, and when any one of the grid electrodes 46 becomes a disconnection T, In this case, the generated charges are not collected by the main electrode 47 and thus disappear. Therefore, a problem in which the photoelectric conversion efficiency decreases rather rapidly occurs. This is caused by the same problem even when forming two patterns in which each grid electrode meets in a direction orthogonal to the main electrode as shown in (a) above.

The present invention has been made to solve the above problems, an object of the present invention is to connect the part or all of the finger line formed on the front of the solar cell so that when the finger line is disconnected, electrons can be collected by the bus electrode. Thus, the problem of reducing the effective photovoltaic area due to the electrode disconnection is remarkably eliminated, and the reduction of the fill factor of the solar cell due to the disconnection can be prevented, and the reduction of the photoelectric conversion efficiency due to the disconnection can be minimized. It is to provide a pattern structure of the front electrode.

The present invention is a configuration for solving the above problems, provided with a front pattern electrode on a silicon substrate constituting a solar cell, the finger line to form the front pattern electrode and the auxiliary finger connecting each finger line It provides a front pattern electrode structure of a solar cell comprising at least one line. This prevents the loss of charges due to electrode breaks, thereby preventing the reduction of the effective photovoltaic region, preventing the reduction of the fill factor, and excluding the reduction of the photoelectric conversion efficiency.

In such a structure of connecting the finger lines may include a variety of ways to connect all or a portion of the finger line, in particular, as an aspect for this, the auxiliary finger line is formed on the outer side portion of the finger line to form a front pattern electrode To be possible. As a result, the above-described prevention of the loss of electric charges can be solved in addition to the problem of reducing the effective photovoltaic region due to overconcentration of the finger line.

In particular, the manner in which the finger lines are connected may be variously changed, and most preferably, the auxiliary finger lines may be arranged to connect at least one or more spaced intervals of neighboring finger lines. That is, when taking a horizontally formed structure as an example, it means to form a structure that forms an auxiliary finger line that can connect the spaced spaces to either the outermost or the inner portion of the neighboring finger line.

Such a structure may be formed of at least one finger line cell structure that connects spaced spaces of neighboring finger lines. In addition, in addition to the auxiliary structure can be modified in various structures according to the connection structure of the finger, in addition to the finger finger line cell structure, formed in a zigzag connection structure, irregular connection type structure, or at least one selected from these combinations It is also possible to form the structure.

In addition, the auxiliary finger line may be formed of the same material as the finger line, and even if formed by further comprising a bus bar that electrically connects the finger lines, the material of the bus bar may be formed of the same material as the finger line. have.

Of course, the solar cell including the structure of the above-described front pattern electrode can be configured. Specifically, a finger line pattern for forming a back electrode and a front pattern electrode on a silicon substrate having p-type and n-type regions and a p-n-type junction region; It is configured to include a bus bar for electrically connecting the finger lines, it can be formed by including the front pattern electrode structure of the solar cell described above as an embodiment of the present invention.

According to the present invention, by connecting some or all of the finger line formed on the front surface of the solar cell, the electrons can be collected by the bus electrode when the finger line is disconnected, thereby reducing the effective photovoltaic region due to the electrode disconnection. It is remarkably removed, prevents reduction of the fill factor of the solar cell due to disconnection, and minimizes the reduction of photoelectric conversion efficiency due to disconnection.

Hereinafter, with reference to the accompanying drawings will be described a specific configuration and operation according to the present invention. (Effective photovoltaic region in the present invention is capable of generating electricity by effectively collecting and transferring the charge generated by receiving sunlight. Defined as an area.)

2A to 2C, this illustrates an embodiment of a structure of a finger line of a front pattern electrode of a solar cell and an introduction structure of an auxiliary finger line connecting the finger line.

The present invention has a front electrode pattern structure including at least one finger line 110 for forming a front pattern electrode on the silicon substrate constituting the solar cell and at least one auxiliary finger line 120 for connecting the finger line. That's the point. Of course, it is preferable to further include a bus bar 130 for electrically connecting and connecting each finger line.

As shown in FIG. 2A, the auxiliary finger line according to the present invention has a structure in which one finger is formed by connecting neighboring finger lines among a plurality of horizontal finger lines 110 (hereinafter, 'fingerline cells'). It can be formed by forming a structure). Of course, a plurality of independent finger line cells FC are formed in the structure of FIG. 2A, and a bus bar 130 is connected to a central portion of the finger line cells.

In addition, as shown in Figure 2b, it may also be formed of a structure that connects the outermost edge of the finger line 110 to the auxiliary finger line 120 in a zigzag form (hereinafter referred to as 'zigzag-shaped structure') of course. to be. In another modified example, the auxiliary finger line 120 of FIG. 2C may be formed in a structure that connects the outermost side of the finger line 110 (hereinafter, referred to as a “closed structure”). Of course, the auxiliary finger line may be formed of the same material as the finger line.

In any case, the gist of the present invention includes realizing a structure in which loss of electric charge is prevented even when disconnection of the finger line occurs by connecting at least one or more portions of the basic finger line with an auxiliary finger line. However, in a preferred embodiment of the present invention, it is more preferable to form a 'fingerline cell structure' or a 'zigzag structure' rather than a 'closed structure' connecting the outermost sides of the finger line 110 described above. desirable. This is because the closed structure also improves the light collection efficiency due to disconnection compared to the prior art, but the path of charge collection is not concentrated, and the loss of electrons is reduced by the line resistance of each line (finger line). This is because the phenomenon that occurs is also provided. The operation of the connection structure of the finger line according to the present invention as described above will be described in detail with reference to FIG.

3A illustrates the problem of the conventional finger line and the operation of various modifications of the structure in which the finger line according to the present invention is connected to the auxiliary finger line.

(a) is a conceptual diagram schematically showing the structure of a conventional finger line, the conventional finger line 110 is connected to the bus bar 130. However, when disconnection (T) occurs in the manufacturing process on any one finger line 111, the charge generated in the disconnection (T) region is not transmitted to the bus bar 111, as shown, the charge is lost The problem arises. (So the finger line of the disconnected part will be calculated as the reactive photovoltaic region.)

(b) is an embodiment according to the present invention, in addition to the bus bar 130 for electrically connecting the finger line 110 and each finger line, as a structure having an auxiliary finger line for connecting a partial region of each finger line Is a conceptual diagram of one formed with the above-described 'fingerline cell' structure.

In this case, when disconnection (T) occurs at a specific location of the finger line, it is connected to the auxiliary finger line can be moved to the bus bar. This enables the disconnection region to be used as an effective photovoltaic region without a separate repair process, and prevents the decrease of the fill factor of the solar cell even when the disconnection occurs, and also prevents the photoelectric conversion efficiency from decreasing. .

(c) illustrates a structure in which the auxiliary finger line 120 is formed on the finger line 110 in a zigzag form, that is, a zigzag structure as an embodiment according to the present invention. In addition, even when disconnection T occurs at a specific location, a structure in which no charge is transmitted to the bus bar 130 can be implemented.

(d) is an embodiment according to the present invention, which shows a structure in which the outer side of the finger line 110 is entirely connected to the auxiliary finger line 120, that is, a 'closed structure', which is also a disconnection (T) Even if) is present, the charge is transferred to the busbar 130. However, as described above, the closed type structure has improved light conversion efficiency compared to the prior art, but when the entire finger line is connected, the charge collecting path is not concentrated, and the line resistance of each finger line is used. There is also a problem of loss of charge. That is, in the above-described 'fingerline cell' structure or the 'zigzag' structure, even if a disconnection part occurs, the electric charges in the vicinity are collected by the bus electrode only through one finger line, so that it is efficiently collected without the influence of the wire terms of the other finger lines. You have concentration. However, in the 'closed structure', the electric charges generated in the disconnected portion can move in any path of the plurality of finger lines (ⅰ, ii, ⅲ), and thus the loss of electric charges is also affected by the line resistance of each finger line. Will occur.

In addition, in the closed structure, the light receiving area is disadvantageous compared with the zigzag type or the finger cell type. Specifically, the line width of the finger is 0.1 mm, the number of fingers is 56 and the length of the finger is 153.5 mm. The structure has a shading loss of 14.82mm ² compared with the zigzag structure, and the consumption of material is much higher.

Of course, the light conversion efficiency of the closed structure compared to the prior art has a synergistic effect, but the most preferred embodiment according to the present invention will be referred to as a finger line cell structure or a zigzag structure.

Looking at this in more detail, Figure 3b is a comparison table comparing the solar cell efficiency of the zigzag-like structure, fingerline cell structure and closed structure as a preferred embodiment according to the present invention compared to the conventional open structure.

According to the table shown, as shown in the results of Examples 1 and 2, and Examples 4 and 5, Examples 7 and 8 according to the present invention, compared to the solar cell efficiency shown in Comparative Examples 1 to 4 It can be seen that the type structure and the fingerline cell structure exhibit superior solar cell efficiency, and the efficiency of the closed type structure may be partially increased as compared to the open type structure. Therefore, a zigzag and finger cell type structure having a line width of 120 μm or less based on a 156 × 156 mm cell according to the present invention is preferable as a finger line and an auxiliary finger line pattern structure of the front electrode of the solar cell. According to the example, the zigzag type finger cell structure in the range of 60 ~ 120㎛ can exhibit a remarkable efficiency in terms of solar cell efficiency, it can be seen that more preferable.

In the above-described exception, a structure in which the finger line is connected through the auxiliary finger line to remove the influence of the disconnection may be variously modified, and in particular, the above-described regular rule and standard connection structure (finger line cell structure, zigzag connection structure) In addition to the structure of connecting only one outer surface of the finger line, etc.) of course, it can also be formed in an irregular connection structure. In addition, it is also possible to form a structure that implements a combination of the standard connection structure (fingerline cell structure, zigzag connection structure, etc.) and irregular connection structure. In conclusion, according to the present invention, any structure of the entire fingerline connected to the auxiliary fingerline to solve the problem caused by disconnection will all be included in the gist of the present invention.

4A and 4B, FIG. 4A shows a front electrode pattern between a structure having only a general finger line and a structure implementing the finger line structure according to the present invention, to fabricate a solar cell, thereby improving efficiency and variation. This is a result of comparing the decrease of.

In this comparative example, the structure formed by the finger line cell structure according to the present invention was formed by the front pattern electrode, the line width of the finger is 100㎛, the number of fingers is 56, the line width of the bus bar is 2mm, the overall pattern The area has a pattern structure of 153.5 mm x 153.5 mm, and based on this pattern structure, a cell was fabricated using a polycrystalline wafer of 156 x 156 mm, and the comparison was made after 19 sheets of each group were compared. .)

Looking at Figure 4a, it can be seen that the width of the deviation is quite large, the efficiency average is 13.7%. This can be seen that the disconnection of the finger line occurs in the printing, drying and firing process, the effect is increased and the efficiency is low.

Looking at Figure 4b, as a result of minimizing the impact of the disconnection with the secondary finger line according to the present invention, it can be seen that the efficiency average is 14.7%, the deviation is also significantly lowered to 0.14%. This is to compensate for the effect of the disconnection by the formation of the auxiliary finger line pattern to reduce the fill factor, it will be said to clearly show the result of minimizing the efficiency reduction.

In the foregoing detailed description of the present invention, specific examples have been described. However, various modifications are possible within the scope of the present invention. The technical idea of the present invention should not be limited to the embodiments of the present invention but should be determined by the equivalents of the claims and the claims.

1A is a conceptual diagram illustrating a general structure of a solar cell, and FIG. 1B illustrates an arrangement structure of finger lines according to the prior art, and FIG. 1C is a conceptual diagram illustrating a technique of narrowing the line width of the finger line according to the prior art. 1D is a plan view illustrating a pattern structure of a conventional front electrode.

2A to 2C illustrate examples of formation of a pattern of a front pattern electrode and an auxiliary finger line according to the present invention.

3a and 3b are comparative views showing the difference in operation of the front pattern electrode according to the prior art and the present invention.

4A and 4B are comparative graphs showing the effects of the present invention through comparison of efficiency and deviation between the prior art and the front pattern electrode according to the present invention.

Claims (8)

The front pattern electrode is provided on the silicon substrate constituting the solar cell, A finger line forming the front pattern electrode; And at least one auxiliary finger line connecting each of the finger lines. The method according to claim 1, The auxiliary finger line is a front pattern electrode structure of a solar cell, characterized in that to form at least one finger line cell connecting the spaced space of the neighboring finger line. The method according to claim 1, The auxiliary finger line is a front pattern electrode structure of a solar cell, characterized in that arranged in a zigzag structure to connect at least one or more spaced intervals of the adjacent finger line. The method according to claim 1, The auxiliary finger line is a front pattern electrode structure of a solar cell, characterized in that formed on the outer side portion of the finger line to form a front pattern electrode. The method according to claim 1, The front pattern electrode is formed with an auxiliary finger line connecting the adjacent finger line, The front pattern electrode structure of a solar cell, characterized in that at least one structure selected from the finger finger line cell, zigzag structure, irregular connection type structure is combined. The method according to any one of claims 1 to 5, The auxiliary finger line is a front pattern electrode structure of a solar cell, characterized in that formed of the same material as the finger line. The method according to any one of claims 1 to 5, And a bus bar electrically connecting the finger lines. a finger line pattern forming a back electrode and a front pattern electrode on a silicon substrate having p-type and n-type regions and a p-n-type junction region; A bus bar electrically connecting the finger lines; Consists of including The solar cell comprising a front pattern electrode structure of the solar cell of claim 1 to 5.

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