KR101034178B1 - Front Electrode pattern of a solar cell And Solar Cell Having The Same - Google Patents

Abstract

The present invention can reduce the loss due to the resistive component and the loss due to the shading by inserting a secondary electrode of a specific structure to reduce the length of the finger electrode and open some regions. Provided are an electrode structure of a solar cell and a solar cell having the same, which can improve efficiency reduction and increase an aperture ratio, thereby remarkably improving solar cell efficiency.

Solar cells, electrode pattern

Description

Front electrode structure of solar cell and solar cell having same {Front Electrode pattern of a solar cell And Solar Cell Having The Same}

The present invention relates to a front electrode structure of a solar cell and a solar cell having the same.

A solar cell is a semiconductor device that absorbs solar energy incident on a cell and converts it into electrical energy. The solar cell has a p-n junction form, and its basic structure is the same as that of a diode.

When light is incident on the solar cell, the incident light is absorbed by the solar cell and interacts with materials constituting the semiconductor of the solar cell. As a result, electrons and holes, which are minority carriers, are formed, and they move to both electrodes formed and connected in a predetermined pattern on the substrate to obtain an electromotive force.

Currently, the most commercially available crystalline silicon solar cells can be largely divided into single crystal and polycrystalline forms. The monocrystalline material is high in purity and low in crystal defect density, which is high in efficiency but relatively expensive. The polycrystalline material is generally inexpensive due to its low purity and low cost in terms of cost. Used.

Since solar cells are devices that convert solar energy into electrical energy, it is necessary to support electrode design and manufacturing of cells to generate a large number of electron-hole pairs by absorbing sunlight as much as possible. .

 An electrode having a metal component is formed on the front surface of the solar cell to collect charges generated by incident sunlight as shown in FIG. 1. The metal electrode is generally composed of a grid, which is a finger electrode, and a bus bar, which is a rod-shaped main electrode electrically connected to the grid. Since the metal electrode does not transmit sunlight to the substrate but reflects the sunlight, a shading loss occurs that reduces the efficiency of the solar cell. Therefore, in order to reduce such a loss, the electrode line width is reduced to minimize the contact area, but when the electrode width is too small, the electrical resistance is generated because the electrode resistance itself becomes large. That is, the structure of the electrode formed on the front surface of the solar cell requires a high aperture ratio in order to receive a lot of incident sunlight and at the same time an optimal pattern that can minimize the resistance loss and shading loss.

The main factors that determine the photoelectric conversion efficiency of the solar cell are the open voltage (Voc), the short-circuit current (Isc), the fill factor (FF), the series resistance (Rs), the parallel resistance (Rsh). Where Voc refers to the voltage across the cell in an open state with no load connected at constant temperature and sunshine intensity, and Isc refers to the current output from the cell in a short circuit at constant temperature and sunshine intensity. FF is a measure of how much energy [Watt] a cell can produce based on the solar energy [Watt] incident from the sun. When the fill factor is 100%, the IV curve shows a perfect square shape, and multiplies only the values of Isc and Voc to obtain the ideal power (Pmax), but the fill factor is 70 to 80 due to the series resistance and parallel resistance inside the cell. It will fall to the% level, making it difficult to produce sufficient Pmax. Of the factors that lower the fill factor, in particular the series resistance portion is important, and usually the series resistance has a large influence on Isc.

2 illustrates the series resistance and shading portion of a conventional polycrystalline silicon solar cell. As shown in Fig. 2, the series resistance is composed of the sum of the substrate resistance, the contact resistance of silicon and the front electrode, the emitter resistance, and the resistance of the electrode metal itself. In this case, the aperture ratio and the series resistance, which are the parts exposed to sunlight according to the front electrode pattern, are highly correlated, and therefore, special care must be taken when designing the front electrode pattern.

The change in efficiency caused by the design change of solar cell front electrode pattern can be used to calculate the resistive and shading loss using the following general power loss formula, which can indirectly predict the trend.

1.Due to the shading

2.Emitted by the sheet resistance of the emitter layer

3. Contact Resistance Loss (Between Emitter and the metallization Finger)

4. Series resistance of a finger

5. Series resistance of a bus-bar

Where a = finger-finger distance

d = finger electrode line width

j _mpp = Max. Power point current density

U _{mppj mpp} = Max. Power point voltage

ρ _b = Tabbed bus-bar line resistivity

ρ _c = Specific contact resistance

ρ _f = Finger sheet resistivity

ρ _sh = Sheet resistance of n-emitter

3 is a schematic diagram of a conventional pattern of the front electrode, showing a pattern composed of a dense finger electrode 102 and a bus bar electrode 101 connected thereto. In addition, various patterns are known in relation to the pattern of the front electrode. However, only fragmentary means such as simply adjusting the width of the finger electrode or the area of the front electrode or increasing the number of finger electrodes are disclosed.

The known patterns generally show a method of improving the efficiency by adjusting the width and the light receiving area of the finger electrode, but there is a problem in that the electrode pattern is limited within the range of not limiting the aperture ratio because the line width is 100 μm or more. . In addition, in order to reduce the finger width, a lithography method, a laser transfer method or the like has been proposed in the process, but there is a problem in that the production cost increases.

An object of the present invention is to solve the problems as described above, to maintain the advantage of implementing the fine line width by introducing an offset method and the like, the finger length by the insertion of the secondary electrode which is the middle electrode of the finger electrode and busbar electrode The purpose is to design an electrode pattern that can maximize the photoelectric conversion efficiency by minimizing the resistive loss and shading loss, and as a result, to provide an electrode pattern that can achieve higher efficiency than conventional commercial patterns.

As a means for solving the above problems,

The present invention provides an electrode structure of a solar cell having a semiconductor substrate, a plurality of finger electrodes formed on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes arranged in the same direction as the plurality of finger electrodes. The present invention provides an electrode structure of a solar cell having a plurality of secondary electrodes connected to at least one of the plurality of busbar electrodes and connected to a plurality of finger electrodes.

The present invention also provides an electrode structure of a solar cell, wherein a part of all or part of a finger electrode connected between the secondary electrodes is opened.

In addition, the finger electrode provides a distance between the electrode structure of the solar cell, characterized in that 1.5 to 3mm.

In addition, the line width of the finger electrode provides an electrode structure of the solar cell, characterized in that less than 50 ~ 100㎛.

In addition, the line width of the bus bar electrode provides an electrode structure of the solar cell, characterized in that 1.5mm to 2mm.

In addition, the line width of the secondary electrode is greater than the line width of the finger electrode, and provides an electrode structure of the solar cell, characterized in that less than the line width of the bus bar electrode.

The present invention also provides an electrode structure of a solar cell, wherein the aperture ratio of the electrode pattern is in a range of 90 to 95%.

The present invention also provides a solar cell substrate having a semiconductor substrate, a plurality of finger electrodes formed on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes connected to the plurality of finger electrodes. Provided is an electrode structure of a solar cell provided between a plurality of busbar electrodes selected from among busbar electrodes or between a busbar electrode and a substrate side end, and having a plurality of finger electrodes and an auxiliary electrode connected to at least one busbar electrode.

In addition, the present invention provides an electrode structure of a solar cell, wherein a part of all or part of finger electrodes connected between bus electrodes is opened to reduce loss due to resistance and loss due to shading.

The present invention also provides a solar cell, wherein the front electrode is provided on the upper portion of the substrate and the rear electrode is provided on the lower surface of the substrate, wherein the front electrode has the electrode structure of the solar cell described above. .

The solar cell top electrode pattern designed by the present invention has a line width of the finger electrode is 50 ~ 100㎛, due to the effect of the fine line width can reduce the light shielding component compared to commercial products to increase the aperture ratio. In addition, the insertion of the secondary electrode reduces the length of the finger electrode and opens some regions, thereby reducing the loss due to the resistive component and the loss due to the shading, thereby further improving solar cell efficiency.

Hereinafter, the present invention will be described in more detail with reference to the drawings and embodiments. The following descriptions are for specific examples of the present invention, but are not intended to limit the scope of the rights set forth in the claims, even though they are assertive or limitative.

Prior to the description, in the present invention, after designing the electrode pattern, the evaluation method of the electrode pattern was performed according to the flowchart of FIG. 4, and in the evaluation method for comparison of the same conditions as the general-purpose type shown in FIG. Finger width, finger spacing, and solar cell substrate size were designed under the same conditions, and then efficiency simulation was conducted.

In addition, for comparison under the same conditions, the electrical data applied to the simulation formula were analyzed with general values of general-purpose products as follows.

J _mpp = max power current density: 32mA / cm ²

V _mpp = max power point voltage: 547mV

ρ _b = Tabbed bus bar line resistivity: 0.94 mΩcm

ρ _c = specific contact resistance: 5mΩcm ²

ρ _f = finger sheet resistivity: 7.2mΩ / □

ρ _sh = Sheet resistance: 50Ω / □

5 is a schematic plan view of the electrode structure of the solar cell according to an embodiment of the present invention. As shown, an electrode structure of a solar cell according to an embodiment of the present invention is the same as the semiconductor substrate, the plurality of finger electrodes 10 formed on at least one surface of the semiconductor substrate, and the plurality of finger electrodes 10. An electrode structure of a solar cell having a plurality of bus bar electrodes 20 arranged in a direction, and connected to at least one of the plurality of bus bar electrodes 20, and a plurality of finger electrodes 10. And an auxiliary electrode 21 to be connected thereto.

In the electrode design, when the distance between the finger electrodes is wide, there are many obstacles for the charge generated at the p-n junction to move to the finger, thereby increasing the series resistance, and as a result, the short circuit current value may be lowered. In particular, in the case of a polycrystalline wafer, there are many grain boundaries, which may cause a problem of increasing charge traps due to defects. On the other hand, if there are many fingers, the distance from which the generated charges go to the finger is shortened, and thus the probability that the generated charges are trapped in the defects is reduced by that amount, but the rate of shielding of the sunlight is increased, resulting in a small amount of charge generation. This may occur, but the present invention has a breakthrough configuration that can lower the shielding ratio while lowering the series resistance.

The finger electrode 10 and the bus bar electrode 20 are distinguished from each other by being arranged in the same direction. Here, the same direction includes not only the parallel arrangements as shown in FIG. 5, but also the crossing angles between the finger electrodes 10 and the busbar electrodes 20 at an angle of 45 ° or less, even if not parallel.

In addition, as shown in FIG. 5, the finger electrode 10 is connected to the busbar electrode 20 by the secondary electrode 21, and the secondary electrode 21 is arranged in a direction perpendicular to the finger electrode 10. . In this case, the vertical direction includes not only the secondary electrodes 21 and the finger electrodes 10 intersecting at 90 degrees but also intersecting at least 45 degrees.

In addition, as shown in FIG. 5, it is more preferable to open (part D of the drawing) a part of all (FIG. 5) or part (not shown) of the finger electrode 10 connected between the auxiliary electrodes 21. desirable. By such a configuration, the shading loss is reduced by compensating for the reduction of the aperture ratio caused by the insertion of the auxiliary electrode 21 and the resistance loss of the finger electrode 10 to reduce the pattern of the solar cell having high photoelectric conversion efficiency. You can get it.

The open portion D of the finger electrode 10 is preferable because the center between the two secondary electrodes 21 can optimally reduce the resistance loss. When opening the finger electrode 10, the opening length is preferably within the range of the finger electrode interval. When the range is widened, the collection path of the carriers generated during photoelectric conversion is too far away, thereby reducing the efficiency of the solar cell. In addition, when the opening length becomes too narrow, two finger electrodes may be connected to each other by a spread phenomenon occurring after printing-firing of the electrode, thereby increasing resistance loss.

In addition, the auxiliary electrodes 21 may be interconnected, but may not be interconnected. The secondary electrodes 21 are connected to the busbar electrodes 20 to reduce the resistance loss, and when the secondary electrodes 21 are interconnected, the shading loss is increased.

The distance between the finger electrodes and the line width of each electrode is important in the electrode pattern design, the distance between the finger electrodes is preferably 1.5 to 3mm. If the finger spacing is less than 1.5, it is effective for the minimum charge transfer distance to reduce the amount of charge trapped in the grain boundary defect in the polycrystalline substrate, but the aperture ratio is reduced to less than 90%, which may cause a problem that the amount of generated charge itself becomes small. . On the other hand, when the finger spacing exceeds 3.0 mm, the incident sunlight increases, thereby increasing the amount of generated charge itself, but the generated charge is moved to the finger and the moving distance that is collected is increased, so that the moving charge is a polycrystalline cell. Trap may be lost in the back.

The line width of the finger electrode is preferably in the range of 50 ~ 100㎛. If the line width of the finger electrode exceeds 100㎛ the loss due to the resistance is reduced, but the loss due to the shading is increased that much to reduce the overall efficiency. On the contrary, the loss due to the shading is reduced at the line width of less than 50 μm, but the loss due to the resistive component is relatively increased so as to reduce the overall efficiency.

It is preferable that the line width of the busbar electrode is 1.5 mm to 2 mm, and the line width of the secondary electrode is greater than or equal to the finger electrode line width and smaller than the line width of the bus bar electrode.

The implementation of the fine line width of the finger electrode can be solved by using an offset printing method. That is, the electrode line width of about 80 to 100 μm can be realized by a general technique of screen printing. However, the fine line width of less than 80 μm is preferably applied to various pattern printing methods such as offset printing.

As a result of the experiment, it was confirmed that even if the opening ratio of the electrode pattern was in the range of 90 to 95%, resistance loss was small and very excellent efficiency could be obtained. If the aperture ratio is less than 90%, the rate of incidence of sunlight itself is small, and thus the amount of charge generated in the substrate is small. If the aperture ratio is greater than 95%, the generated charge increases, but the charge in the protective film or grain boundary is increased. As the probability of trapping increases, the cell efficiency may actually decrease, resulting in an optimal range.

6 and 7 are schematic plan views of the electrode structure of the solar cell according to another embodiment of the present invention. As illustrated, a semiconductor substrate, a plurality of finger electrodes 10 formed on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes 20 connected to the plurality of finger electrodes 10 are provided. A solar cell substrate comprising a plurality of finger electrodes 10 and at least between two busbar electrodes 20 selected from among the plurality of busbar electrodes 20 or between busbar electrodes 20 and a substrate side end. It is characterized in that the electrode structure of the solar cell provided with a secondary electrode 21 connected to at least one bus bar electrode 20.

As shown in FIGS. 6 and 7, the bus bar electrode 20 and the finger electrode 10 are arranged in the vertical direction. In this case, the vertical direction includes not only the busbar electrode 20 and the finger electrode 10 intersecting at 90 ° but also being arranged to intersect at least 45 °.

As illustrated in FIGS. 6 and 7, the auxiliary electrode 21 may be located between the busbar electrodes 20 or may be located between the busbar electrode 20 and the substrate side end. The secondary electrode 21 is connected to the plurality of finger electrodes 10 and at least one bus bar electrode 20. The secondary electrodes 21 may be interconnected as in FIG. 6, or may not be interconnected as in FIG. 7.

In addition, based on the results derived in the above-described embodiment, as shown in FIG. 7, a part (D part of the drawing) of all or part of the finger electrode 10 connected between the auxiliary electrodes 21 is opened. By doing so, a more efficient solar cell pattern can be obtained. The open area and open width of the finger electrode 10 are as described above.

In addition, it is preferable that the distance between the finger electrodes, the line width of each electrode, and the aperture ratio of the electrode pattern also depend on the result derived from the above-described embodiment. That is, the distance between the finger electrodes is preferably 1.5 to 3mm, the line width of the finger electrode is 50 ~ 100㎛ or less, the line width of the bus bar electrode 20 is preferably 1.5mm to 2mm, the secondary electrode 21 ) Has a line width greater than or equal to the finger electrode line width and smaller than the line width of the bus bar electrode 20. Further, even if the opening ratio of the electrode pattern is in the range of 90 to 95%, excellent efficiency can be obtained.

The present invention also provides a solar cell, wherein the front electrode is provided on the upper portion of the substrate and the rear electrode is provided on the lower surface of the substrate, wherein the front electrode has the electrode structure of the solar cell described above. . Since the configuration of the solar cell is well known in the art, the description is omitted and the present invention can be made by selecting a known configuration and is not limited.

<Examples>

The design of the pattern was designed using a design program capable of accurate numerical input and the pattern was designed and tested by efficiency measurement simulation methods commonly used in the art. The silicon substrate size is applicable to all cells such as 5 inches and 6 inches, and the electrode pattern may also change in quantity and length according to the change in the substrate size. The efficiency calculation results exemplified in the present invention relate to design evaluation on a 5 inch basis, but the present invention is not limited to the 5 inch substrate size.

First, the shape of the busbar electrode and the secondary electrode was designed, and then the finger electrode pattern was designed. In addition, in order to calculate the shading loss caused by the busbar electrode, the area of the busbar electrode and the secondary electrode was calculated and substituted into the simulation formula. Next, after analyzing the length and quantity of the fingers, the losses due to the finger electrodes were calculated. Then, the losses due to the resistive and shading components by the finger electrodes and the shading losses by the bus bars were summed up to calculate the efficiency under the assumption of the solar spectral incidence condition of AM1.5.

One embodiment pattern designed and presented in the present invention is shown in Figure 5 (example 1), Figure 6 (example 2), Figure 7 (example 3), the efficiency calculation results are shown in FIG.

In FIG. 8, the results of efficiency calculations when the 80 μm finger electrode line width and the finger electrode spacing were 2.77 mm were compared with those of current commercial products (FIG. 3 pattern). As shown in the graph of Figure 8 it can be seen that the efficiency of the pattern according to the design example of the present invention increases from about 0.4% to about 0.8% or more. For solar cells, it is clear that the difference in efficiency is more than 0.4%.

1 illustrates a conventional silicon solar cell;

Figure 2 shows a conventional series resistor and shading portion,

3 is a schematic diagram of a front electrode pattern of a conventional K solar cell commercially available,

4 is a design and test flow diagram related to the present invention,

5 is a view related to Example 1 of an electrode pattern according to an embodiment of the present invention;

6 is a view related to Example 2 of an electrode pattern according to another embodiment of the present invention;

7 is a view related to Example 3 of an electrode pattern according to another embodiment of the present invention;

8 is a graph illustrating efficiency comparison between existing commercial patterns and electrode patterns provided in the present invention.

** Description of the main symbols in the drawings **

10: finger electrode

20: busbar electrode

21: secondary electrode

Claims (10)

An electrode structure of a solar cell having a semiconductor substrate, a plurality of finger electrodes formed on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes arranged in the same direction as the plurality of finger electrodes, A plurality of auxiliary electrodes connected to at least one of the plurality of busbar electrodes and connected to the plurality of finger electrodes, The electrode structure of the solar cell, characterized in that the opening of all or part of the finger electrode connected between the secondary electrode. delete The electrode structure of claim 1, wherein the distance between the finger electrodes is 1.5 to 3 mm. The electrode structure of claim 1, wherein the line width of the finger electrode is 50 to 100 μm or less. The electrode structure of claim 1, wherein the busbar electrode has a line width of 1.5 mm to 2 mm. The electrode structure of claim 1, wherein a line width of the secondary electrode is greater than or equal to the finger electrode line width and smaller than a line width of the bus bar electrode. The electrode structure of a solar cell according to claim 1, wherein the opening ratio of the semiconductor substrate on which the busbar electrode, the finger electrode and the auxiliary electrode is formed is in a range of 90 to 95%. A solar cell substrate having a semiconductor substrate, a plurality of finger electrodes formed on at least one surface of the semiconductor substrate, and a plurality of bus bar electrodes connected to the plurality of finger electrodes. Among the plurality of busbar electrodes is provided between the two busbar electrodes or between the busbar electrode and the substrate side end is provided with a plurality of finger electrodes and the secondary electrode connected to at least one busbar electrode, An electrode structure of a solar cell, wherein a part of all or part of a finger electrode connected between bus electrodes is opened to reduce loss due to resistance and shading loss. delete In a solar cell provided with a front electrode on the upper portion of the substrate and a rear electrode on the lower surface of the substrate, The said front electrode has the electrode structure of the solar cell of any one of Claim 1, 3-8.

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