KR20160024153A - Paste composition for solar cell electrode and solar cell - Google Patents

Abstract

A paste composition for a solar cell electrode used in a solar cell electrode according to an embodiment of the present invention comprises a thallium compound. The paste composition for a solar cell electrode can comprise thallium oxide. The paste composition according to the embodiment smoothens a fire-through process by lead oxide, and maintains excellent contact properties of the electrode and a semiconductor substrate or a conductive area.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a paste composition for a solar cell electrode,

The present invention relates to a paste composition for a solar cell electrode and a solar cell.

With the recent depletion of existing energy sources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar cells are attracting attention as a next-generation battery that converts solar energy into electric energy.

In such solar cells, various layers and electrodes can be fabricated by design. However, solar cell efficiency can be determined by the design of these various layers and electrodes. In order to commercialize the solar cell, it is required to overcome the low efficiency and to improve the characteristics of various layers and electrodes to maximize the efficiency of the solar cell.

Here, various characteristics of the electrode, manufacturing cost, and the like depend on the composition of the paste composition for the solar cell electrode for forming the electrode of the solar cell. Accordingly, it is required to develop a paste composition for a solar cell electrode that can improve the characteristics of an electrode.

The present invention provides a paste composition for a solar cell electrode capable of improving the characteristics of an electrode.

The present invention also provides a solar cell having an electrode having excellent characteristics.

The paste composition for a solar cell electrode used in a solar cell electrode according to an embodiment of the present invention includes a thallium compound. At this time, the paste composition for a solar cell electrode may contain thallium oxide.

A solar cell according to an embodiment of the present invention includes a photoelectric conversion unit; And an electrode connected to the photoelectric conversion unit, wherein the electrode includes lead and thallium.

The paste composition according to the present embodiment can smooth the piercing through the lead oxide and keep the contact characteristics between the electrode and the semiconductor substrate or the conductive type region at a good level. The glass transition temperature of the glass frit can be lowered and the glass stability at low temperature can be improved while reducing the content of lead oxide including thallium compounds (particularly, thallium oxide). Thus, even when the firing is performed at a low temperature, the contact characteristics between the electrode and the semiconductor substrate or the conductive type region can be realized uniformly and excellently.

Such a paste composition can be applied to electrodes of solar cells to improve contact properties of electrodes and the like. Particularly, when a solar cell having an n-type base region and a p-type emitter region having a low firing temperature is used as a front electrode connected to the emitter region, the glass stabilization effect can be maximized at a low temperature, The effect can be maximized.

1 is a schematic cross-sectional view illustrating a solar cell according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it is needless to say that the present invention is not limited to these embodiments and can be modified into various forms.

In the drawings, the same reference numerals are used for the same or similar parts throughout the specification. In the drawings, the thickness, the width, and the like are enlarged or reduced in order to make the description more clear, and the thickness, width, etc. of the present invention are not limited to those shown in the drawings.

Wherever certain parts of the specification are referred to as "comprising ", the description does not exclude other parts and may include other parts, unless specifically stated otherwise. Also, when a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, it also includes the case where another portion is located in the middle as well as the other portion. When a portion of a layer, film, region, plate, or the like is referred to as being "directly on" another portion, it means that no other portion is located in the middle.

Hereinafter, a paste composition for a solar cell electrode according to an embodiment of the present invention and a solar cell manufactured using the paste composition will be described in detail with reference to the accompanying drawings. First, an example of a solar cell will be described, and then a paste composition for a solar cell electrode used in the production thereof will be described in more detail.

1 is a schematic cross-sectional view illustrating a solar cell according to an embodiment of the present invention.

1, a solar cell 150 according to the present embodiment includes a substrate 110 (e.g., a semiconductor substrate) 110 (hereinafter, referred to as a " semiconductor substrate " 20 and 30 and electrodes 24 and 34 electrically connected to the conductive regions 20 and 30. The conductive type regions 20 and 30 may include an emitter region 20 and a rear electric field region 30 and the electrodes 24 and 34 may include a first electrode electrically connected to the emitter region 20 24 and a second electrode 34 electrically connected to the rear electric field area 30. In addition, the solar cell 150 may further include an antireflection film 22, a passivation film 32, and the like. A ribbon (not shown) for connection with another solar cell 150 may be disposed on the electrodes 24 and 34. This will be explained in more detail.

The semiconductor substrate 110 may be formed of a crystalline semiconductor. In one example, the semiconductor substrate 110 may be composed of a single crystal or polycrystalline semiconductor (e.g., single crystal or polycrystalline silicon). In particular, the semiconductor substrate 110 may be composed of a single crystal semiconductor (for example, a single crystal semiconductor wafer, more specifically, a single crystal silicon wafer). Thus, when the semiconductor substrate 110 is made of a single crystal semiconductor (for example, a single crystal silicon), the solar cell 150 constitutes a single crystal semiconductor solar cell (for example, a single crystal silicon solar cell). The solar cell 150 based on the semiconductor substrate 110 made of a crystalline semiconductor having a high crystallinity and having few defects can have excellent electrical characteristics.

The front surface and / or the rear surface of the semiconductor substrate 110 may be textured to have irregularities. The irregularities may be, for example, a (111) plane of the semiconductor substrate 110 and may have a pyramid shape having an irregular size. If the surface roughness of the semiconductor substrate 110 is increased due to such irregularities formed on the front surface of the semiconductor substrate 110, the reflectance of light incident through the front surface of the semiconductor substrate 110 can be reduced. Accordingly, the amount of light reaching the pn junction formed by the base region 10 and the emitter region 20 can be increased, thereby minimizing the optical loss. However, the present invention is not limited thereto, and it is also possible that the irregularities due to texturing are not formed on the front surface and the rear surface of the semiconductor substrate 110.

The semiconductor substrate 110 may include a base region 10 having a second conductivity type including a second conductivity type dopant at a relatively low doping concentration. For example, the base region 10 may be located farther from the front surface of the semiconductor substrate 110 than the emitter region 20, or closer to the rear surface. And the base region 10 may be closer to the front surface of the semiconductor substrate 110 than to the rear surface region 30 and further away from the rear surface. However, the present invention is not limited thereto, and it goes without saying that the position of the base region 10 can be changed.

Here, the base region 10 may be formed of a crystalline semiconductor containing a second conductive dopant. In one example, the base region 10 may be composed of a single crystal or a polycrystalline semiconductor (for example, single crystal or polycrystalline silicon) including a second conductive type dopant. In particular, the base region 10 may be comprised of a single crystal semiconductor (e.g., a single crystal semiconductor wafer, more specifically a single crystal silicon wafer) comprising a second conductive dopant.

The second conductivity type may be n-type or p-type. When the base region 10 has an n type, the base region 10 is formed of a single crystal or polycrystalline semiconductor doped with a Group 5 element (P), arsenic (As), bismuth (Bi), antimony (Sb) Lt; / RTI > When the base region 10 has a p-type, the base region 10 is formed of a single crystal or polycrystalline semiconductor doped with boron (B), aluminum (Al), gallium (Ga) Lt; / RTI > As an example, the base region 10 in this embodiment may have an n-type.

However, the present invention is not limited thereto, and the base region 10 and the second conductive dopant may be composed of various materials.

As an example, the base region 10 may be n-type. Then, the emitter region 20 forming the pn junction with the base region 10 has a p-type. When the pn junction is irradiated with light, electrons generated by the photoelectric effect move toward the second surface (hereinafter referred to as "back surface") of the semiconductor substrate 110 and are collected by the second electrode 34, 110 and collected by the first electrode 24. Thereby, electric energy is generated. Then, holes having a slower moving speed than electrons may move to the front surface of the semiconductor substrate 110, rather than the rear surface thereof, thereby improving the conversion efficiency. However, the present invention is not limited thereto, and it is also possible that the base region 10 and the rear electric field region 30 have the p-type and the emitter region 20 has the n-type.

An emitter region 20 having a first conductivity type opposite to the base region 10 may be formed on the front surface of the semiconductor substrate 110. The emitter region 20 forms a pn junction with the base region 10 to form an emitter region for generating carriers by photoelectric conversion.

In this embodiment, the emitter region 20 may be formed as a doped region constituting a part of the semiconductor substrate 110. Accordingly, the emitter region 20 may be formed of a crystalline semiconductor including a first conductive type dopant. In one example, the emitter region 20 may be comprised of a single crystal or polycrystalline semiconductor (e.g., single crystal or polycrystalline silicon) comprising a first conductivity type dopant. In particular, the emitter region 20 may be comprised of a single crystal semiconductor (e.g., a single crystal semiconductor wafer, more specifically a single crystal silicon wafer) comprising a first conductivity type dopant. When the emitter region 20 is formed as a part of the semiconductor substrate 110 in this way, the junction characteristics with the base region 10 can be improved.

However, the present invention is not limited thereto, and the emitter region 20 may be formed separately from the semiconductor substrate 110 on the semiconductor substrate 110. In this case, the emitter region 20 may be formed of a semiconductor layer having a crystal structure different from that of the semiconductor substrate 110 so that the emitter region 20 can be easily formed on the semiconductor substrate 110. For example, the emitter region 20 may be formed of an amorphous semiconductor, a microcrystalline semiconductor, or a polycrystalline semiconductor (for example, amorphous silicon, microcrystalline silicon, or polycrystalline silicon) 1 < / RTI > conductivity type dopant. Various other variations are possible.

The first conductivity type may be p-type or n-type. When the emitter region 20 has a p-type, the emitter region 20 is formed of a single crystal or polycrystalline material doped with boron (B), aluminum (Al), gallium (Ga) May be made of semiconductors. When the emitter region 20 has an n-type, the emitter region 20 is formed of a single crystal or polycrystalline (P) doped with a Group 5 element such as P, As, bismuth, or antimony May be made of semiconductors. However, the present invention is not limited thereto, and various materials may be used as the first conductivity type dopant.

The figure illustrates that the emitter region 20 has a homogeneous structure with a uniformly uniform doping concentration. However, the present invention is not limited thereto. Thus, in another embodiment, the emitter region 20 may have a selective structure. The selective structure has a high doping concentration, a large junction depth, and a low resistance in the portion of the emitter region 20 adjacent to the first electrode 24, and a low doping concentration, a small junction depth, and a high resistance have. As the structure of the emitter region 20, various other structures may be applied.

A rear electric field region 30 having a second conductive type identical to that of the base region 10 and including a second conductive dopant at a higher doping concentration than the base region 10 is formed on the rear surface side of the semiconductor substrate 110 . The back electric field region 30 forms a back surface field to prevent a carrier from being lost by recombination on the surface of the semiconductor substrate 110 (more precisely, the rear surface of the semiconductor substrate 110) .

In this embodiment, the rear electric field region 30 may be a doped region constituting a part of the semiconductor substrate 110. Accordingly, the rear electric field region 30 may be formed of a crystalline semiconductor including a second conductive dopant. In one example, the back electric field region 30 may be composed of a single crystal or polycrystalline semiconductor (for example, single crystal or polycrystalline silicon) including a second conductive type dopant. In particular, the back electric field region 30 may be composed of a single crystal semiconductor (for example, a single crystal semiconductor wafer, more specifically, a single crystal silicon wafer) including a second conductive type dopant. When the rear electric field area 30 is formed as a part of the semiconductor substrate 110 in this way, the junction characteristics with the base area 10 can be improved.

However, the present invention is not limited thereto, and the rear electric field region 30 may be formed separately from the semiconductor substrate 110 on the semiconductor substrate 110. In this case, the rear electric field region 30 may be formed of a semiconductor layer having a crystal structure different from that of the semiconductor substrate 110 so that the rear electric field region 30 can be easily formed on the semiconductor substrate 110. For example, the rear electric field region 30 may be formed of an amorphous semiconductor, a microcrystalline semiconductor, or a polycrystalline semiconductor (for example, amorphous silicon, microcrystalline silicon, or polycrystalline silicon) 2 conductivity type dopant. Various other variations are possible.

The second conductivity type may be n-type or p-type. When the rear electric field area 30 has an n-type, the rear electric field area 30 is formed of a single crystal or polycrystal (P) doped with Group 5 elements such as arsenic (As), bismuth (Bi), antimony (Sb) May be made of semiconductors. When the back electric field region 30 has a p-type, the back electric field region 30 is formed of a single crystal or polycrystal, such as boron (B), aluminum (Al), gallium (Ga) May be made of semiconductors. However, the present invention is not limited thereto, and various materials may be used as the second conductivity type dopant. The second conductive dopant in the rear electric field region 30 may be the same as or different from the second conductive dopant in the base region 10.

In the present embodiment, the back electric field region 30 has a homogeneous structure having a uniform doping concentration as a whole. However, the present invention is not limited thereto. Thus, in another embodiment, the rear field regions 30 may have a selective structure. In the selective structure, it is possible to have a high doping concentration, a large junction depth, and a low resistance in a portion adjacent to the second electrode 34 in the rear electric field area 30 and a low doping concentration, a small junction depth, have. In yet another embodiment, the back electric field region 30 may have a local structure. In the local structure, the rear electric field area 30 may be formed locally corresponding to the portion where the second electrode 34 is formed. Various other structures may be applied to the structure of the rear electric field area 30.

The antireflection film 22 is formed on the front surface of the semiconductor substrate 110 and more precisely on the emitter region 20 formed on or in the semiconductor substrate 110. The first electrode 24 is formed on the passivation film 22 (That is, through the opening) to the emitter region 20.

The antireflection film 22 may be formed substantially entirely on the entire surface of the semiconductor substrate 110 except for the opening corresponding to the first electrode 24.

The antireflective film 22 is formed in contact with the emitter region 20 to passivate defects present in the surface or bulk of the emitter region 20. Accordingly, it is possible to increase the open-circuit voltage (Voc) of the solar cell 150 by removing recombination sites of the minority carriers. Also, the anti-reflection film 22 reduces the reflectance of light incident on the front surface of the semiconductor substrate 110. Accordingly, the amount of light reaching the pn junction formed by the base region 10 and the emitter region 20 can be increased by lowering the reflectance of light incident through the entire surface of the semiconductor substrate 110. Accordingly, the short circuit current Isc of the solar cell 150 can be increased. As described above, the efficiency of the solar cell 150 can be improved by increasing the open-circuit voltage and the short-circuit current of the solar cell 150 with the anti-reflection film 22.

The antireflection film 22 may be formed of various materials. For example, the antireflection film 22 may be a single film selected from the group consisting of a silicon nitride film, a silicon nitride film including hydrogen, a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, MgF ₂ , ZnS, TiO ₂ and CeO ₂ , Layer structure having a combination of at least two layers. In one example, the antireflection film 22 may comprise silicon nitride.

However, the present invention is not limited thereto, and it goes without saying that the anti-reflection film 22 may include various materials. Various films other than the antireflection film 22 may be formed on the semiconductor substrate 110. Other variations are possible.

The first electrode 24 is electrically connected to the emitter region 20 through an opening formed in the antireflection film 22 (i.e., through the antireflection film 22). The first electrode 24 may be formed to have various shapes by various materials. For example, the second electrode 24 may include a plurality of finger electrodes formed in parallel with each other, and a bus bar electrode connecting the finger electrodes.

A passivation film 32 and a second electrode 34 may be formed on the rear surface of the semiconductor substrate 110. The solar cell 150 according to this embodiment has an n-type base region 10 and the second electrode 34 has a shape similar to that of the first electrode 24. That is, the second electrode 34 may have a predetermined pattern, such as having a plurality of finger electrodes and a bus bar electrode connecting them. Accordingly, the solar cell 150 may have a bi-facial solar cell structure in which the light incident through the rear surface can be used together. However, the present invention is not limited thereto, and it is also possible that the second electrode 34 has a shape different from that of the first electrode 24.

The passivation film 32 may be formed substantially on the entire rear surface of the semiconductor substrate 110 except for the portion where the second electrode 34 is formed. This passivation film 32 can pass the defects present on the back surface of the semiconductor substrate 110 to remove recombination sites of the minority carriers. Thus, the open-circuit voltage of the solar cell 150 can be increased.

For example, the passivation film 32 may be formed of any one single film selected from the group consisting of a silicon nitride film, a silicon nitride film including hydrogen, a silicon oxide film, a silicon oxynitride film, MgF ₂ , ZnS, TiO ₂ and CeO ₂ , And may have a combined multilayer structure. However, the present invention is not limited thereto, and it goes without saying that the passivation film 32 may include various materials.

The second electrode 34 is electrically connected to the rear field region 30 through an opening formed in the passivation film 32 (i.e., through the passivation film 32). The second electrode 34 is made of various materials and may have various shapes.

At this time, the first and second electrodes 24 and 34 may be formed, for example, by applying a paste composition containing a conductive material, followed by firing. In particular, the first electrode 24, which is a front electrode positioned on the front surface of the semiconductor substrate 110, may be formed by a fire-through process using a paste composition according to the present embodiment . The term "fire through" refers to a phenomenon that when the paste composition is applied onto an insulating film (for example, the antireflection film 22) located on a conductive type region (for example, the emitter region 20) and baked by heat treatment, Is etched to etch the insulating film to penetrate the insulating film and connect to the conductive type region.

The first electrode 24 made using the paste composition according to the present embodiment may include lead and thallium. Lead is included as a glass frit in the form of lead oxide to assist in firing through the first electrode 24 and thallium is included in the form of a thallium compound as a glass frit or separately to lower the glass transition temperature and improve glass stability . This will be described in more detail.

Hereinafter, the paste composition applicable to the first electrode 24 will be described in detail.

The paste composition according to this embodiment may further include a conductive powder, a glass frit, an organic vehicle, and other additives. At this time, the paste composition contains a thallium compound. As an example, the thallium compound may be thallium oxide. The thallium compound or thallium oxide may be contained in one of the various oxides constituting the glass frit or contained in the paste composition separately from the glass frit. The thallium or thallium oxide can be detected by various methods, such as, for example, an inductively coupled plasma spectrometer (ICP).

Hereinafter, a case where thallium is contained in a glass frit and contained in a paste composition will be described in detail below. In another embodiment, a case where thallium is contained in a paste composition in the form of an additive different from glass frit is described in detail Explain.

In one embodiment, when thallium is included in the glass frit and included in the paste composition, the paste composition is as follows.

The conductive powder may include a metal, a conductive polymer material, and the like. As the metal, silver, aluminum, gold, copper, an alloy including one of them, or the like can be used. As the conductive high molecular material, polypyrrole, polyaniline and the like can be used. At this time, as the conductive powder, silver having high electric conductivity and excellent adhesion property to the ribbon can be used.

In this embodiment, the conductive powder may be contained in an amount of 40 to 95 parts by weight based on 100 parts by weight of the total paste composition. If the weight ratio of the conductive powder is less than 40 parts by weight, the content of the conductive material in the paste composition may be low and the electrical characteristics may be poor. If the weight of the conductive powder is more than 95 parts by weight, the glass frit and the organic vehicle are not sufficiently contained, so that the adhesion force between the electrode and the semiconductor substrate 110 may be lowered and the contact resistance of the electrode may be poor. However, the present invention is not limited thereto, and the weight of the conductive powder may vary.

Such conductive powder may have various shapes such as spherical or non-spherical (plate, vertical or flake). As the conductive powder, single particles may be used, or particles having different particle diameters may be mixed and used.

The glass frit is vitrified at a certain glass transition temperature (Tg) or higher so that sintering of the conductive powder is performed, and the conductive powder and the semiconductor substrate 110 or the emitter region 20 serve to improve adhesion so as to make good contact. In this embodiment, the glass frit is allowed to pass through the antireflection film 22, which is an insulating film, by a firing process during the firing process.

In this embodiment, the glass frit includes lead oxide (e.g., PbO) and thallium oxide (e.g., Tl ₂ O) to effectively lower the glass transition temperature.

Here, the lead oxide facilitates the piercing process through the etching of the antireflection film 22, and improves the sintering property of the conductive powder to have excellent contact characteristics with the semiconductor substrate 110 . The lead oxide has a high solubility of the conductive powder (for example, silver) and can improve the conductivity of the first electrode 24 after firing. For example, lead oxide has a higher solubility of silver than bismuth oxide. Further, the glass transition temperature of the glass frit can be lowered.

The thallium oxide reduces the glass transition temperature of the glass frit and maintains a stable glass state. If the glass transition temperature is lowered as described above, the glass frit can have sufficient fluidity when baked, so that the contact between the semiconductor substrate 110 and the first electrode 24 can be made uniform and homogeneous. At this time, in the case of lead oxide or bismuth oxide, it is possible to lower the glass transition temperature, but it is difficult to maintain a stable glass state, but thallium oxide can maintain a stable glass state while lowering the glass transition temperature. If a stable glass state is provided even at a low temperature by the thallium oxide, stable glass crystallinity and excellent glass forming ability at low temperature can be obtained. Accordingly, it is possible to reproduce characteristics stably during firing, so that the process stability can be greatly improved, and the characteristics of the first electrode 24 of the solar cell 150 can be kept excellent and uniform. On the other hand, if the glass frit does not have a stable glass state, the glass frit can not uniformly sinter the conductive powder at the time of firing, so that the characteristics of the first electrode 24 of the solar cell 150 Can be degraded.

In the present invention, thallium oxide which can maximize the glass stability of the glass frit with a thallium compound is exemplified. However, the present invention is not limited thereto, and various thallium compounds such as thallium nitride, thallium fluoride, and thallium carbide may be used to improve the glass stability.

If the glass frit contains thallium oxide together with the lead oxide as in the present embodiment, contact properties with the semiconductor substrate 110 can be improved by forming a stable glass even at a low temperature while reducing the amount of lead oxide.

At this time, thallium oxide may be contained in an amount of 1 to 90 mol% based on 100 mol% of the entire glass frit. If the amount of the thallium oxide is less than 1 mol%, the effect of the thallium oxide may not be sufficient. If the amount of the thallium oxide exceeds 90 mol%, it may be difficult to be vitrified and the lead oxide content is insufficient, . In order to ensure the content of lead oxide in the glass frit, thallium oxide may be contained in an amount of 1 to 50 mol% (more specifically, 1 to 40 mol%) based on 100 mol% of the entire glass frit. In order to further improve the effect of thallium oxide, thallium oxide may be contained in an amount of 10 to 90 mol% (for example, 10 to 50 mol%, more specifically, 10 to 40 mol%) based on 100 mol% of the entire glass frit.

The glass frit may contain, in addition to the thallium oxide, the remainder as lead oxide. As an example, the lead oxide may be contained in an amount of 10 to 99 mol% based on 100 mol% of the entire glass frit. If the lead oxide is contained in an amount of less than 10 mol%, the paste composition does not sufficiently etch the insulating film of the antireflection film 22 or the like, and fire through may not occur smoothly. If the lead oxide is contained in an amount exceeding 99 mol%, crystallization may occur and vitrification may be difficult to occur.

At this time, by controlling the content of thallium oxide in order to secure the content of lead oxide, lead oxide may be contained in an amount of 10 to 50 mol% or 10 to 60 mol% based on 100 mol% of the entire glass frit. The crystallization of the glass frit can be made more stable in the content of lead oxide. In order to further improve the effect of the thallium oxide, the lead oxide may be contained in an amount of 10 to 90 mol% (for example, 10 to 50 mol% or 10 to 60 mol%) if the thallium oxide is contained in an amount of 10 mol% or more. The content of such lead oxide is determined within a range that ensures sufficient content of thallium oxide and stable occurrence of fire through.

In particular, when the lead oxide is contained in an amount of 10 to 20 mol% of the thallium oxide and the lead oxide is contained in the amount of 80 to 60 mol%, the glass stabilizing effect by the thallium oxide and the etching effect by the lead oxide are sufficiently exhibited, The contact resistance of the contact portion 24 can be minimized.

If the glass frit is made of only thallium oxide and lead oxide, the composition of the glass frit can be simplified to reduce the material cost and simplify the process. However, the present invention is not limited thereto, and the glass frit may include various other glass frit materials other than thallium oxide and lead oxide. In this case also, lead oxide and thallium oxide can be included as main components of the glass frit. Here, the main component means that it is contained in an amount of 50 mol% or more. That is, lead oxides and thallium oxides may be contained in an amount of 50 mol% or more (for example, 50 to 99 mol%) relative to 100 mol% of the entire glass frit, and other glass frit materials may be contained in a total amount of 1 to 50 mol% . Then, the effect of lead oxide and thallium oxide can be further improved, and the effect of other glass frit materials can be sufficiently realized.

(Or network formers), glass modifiers (or network modifiers), intermediates and the like that form the glass with other glass frit materials can do.

Examples of the glass forming agent include silicon oxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), phosphorus oxide (P ₂ O ₅ ), and the like . The glass modifier is a material that cuts the network structure and lowers the melting point (softening temperature), and includes lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), potassium oxide (K ₂ O) have. The intermediate agent may be a glass-forming agent or a glass-forming agent after being influenced by the glass-forming agent. Examples of the intermediate agent include zinc oxide (ZnO) and aluminum oxide (Al ₂ O ₃ ) . However, the present invention is not limited thereto, and various materials can be used as other glass frit materials.

The glass transition temperature of the glass frit according to the present embodiment may be 200 to 400 캜. If the glass transition temperature of the glass frit is less than 200 占 폚, the glass frit may easily crystallize and it may be difficult to maintain the glass state. This may reduce the fluidity in the paste composition during firing, making it difficult to evenly and uniformly contact the first electrode 24 on the semiconductor substrate 110. If the glass transition temperature of the glass frit exceeds 400 캜, the flowability of the glass frit is low and it may be difficult to evenly and uniformly contact the first electrode 24 on the semiconductor substrate 110. In particular, the glass transition temperature of the glass frit may be 200 to 300 캜. This is because the glass transition temperature of the glass frit can be sufficiently lowered by the thallium oxide even if the content of the lead oxide is reduced. That is, in this embodiment, the content of lead oxide including thallium oxide can be lowered to reduce the glass instability, while the glass transition temperature can be lowered and the glass stability can be improved. However, the present invention is not limited thereto, and the glass transition temperature of the glass frit may have various values.

The above-described glass frit is obtained by mixing powders of a material (for example, lead oxide, thallium oxide, and / or other glass frit material) constituting the glass frit, melting the glass frit, cooling it to a predetermined shape Followed by pulverization. For example, after the powder of the material constituting the glass frit is mixed, the glass frit is melted at a temperature of 1000 to 1300 DEG C, dropped in a droplet form, and passed between two rolls to prepare a glass frit in the form of a plate, It can be pulverized.

The glass frit thus produced may have a median particle diameter (D ₅₀ ) of less than or equal to 3 um (e.g., 0.5 um to 3 um), and in one example, a center of 0.5 um to 2 um (more specifically, 0.5 um to 1.7 um) Particle size. Glass frit having a center particle diameter of less than 0.5 탆 may be difficult to manufacture, but a glass frit of less than 0.5 탆 may be used if there is no manufacturing difficulty. If the center diameter of the glass frit exceeds 3 탆, the maximum particle diameter of the glass frit becomes large, so that the glass frit can not be easily vitrified during firing, resulting in poor fluidity. The center diameter of the glass frit can be set to 2 탆 or less, more specifically, 1.7 탆 or less so that the glass frit and the paste composition containing the glass frit can have better properties. However, the present invention is not limited thereto and various modifications are possible.

The glass frit may be contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the entire paste composition. The glass frit can improve the adhesive strength, sintering property and post-processing process characteristics of the solar cell 150 within the range of 0.1 to 10 parts by weight. However, the present invention is not limited thereto, and the content of the glass frit may have various values.

The organic vehicle may be one in which the binder is dissolved in a solvent, and may further contain a defoaming agent, a dispersant, and the like. As the solvent, organic solvents such as terpineol and carbitol can be used. As the binder, a cellulose-based binder may be used.

The organic vehicle may constitute the remainder of the conductive powder, glass frit. In one example, the organic vehicle may be contained in an amount of 2 to 60 parts by weight based on 100 parts by weight of the whole paste composition. Here, if the organic vehicle is contained in an amount of less than 2 parts by weight, the amount of the conductive powder becomes relatively large, and the cost of the paste composition can be increased. If the organic vehicle contains more than 60 parts by weight, the electrical conductivity of the first electrode 24 may be lowered. As an example, 8 to 30 parts by weight of organic vehicle may be included. However, the present invention is not limited thereto, and it goes without saying that the amount of the organic vehicle may vary depending on the amount of the glass frit and the conductive powder.

In addition, the additives may further include a dispersing agent, a thixotropic agent, a leveling agent, an antifoaming agent, and the like. As the dispersant, various materials capable of improving the dispersion characteristics of the conductive powder, the glass frit and the like can be used. As the plasticizer, a polymer / organic material such as urea type, amide type or urethane type may be used, or inorganic type silica may be used. Various agents known as leveling agents, defoaming agents, and the like can be used. Such additives may be included in a total amount of 0.1 to 5 parts by weight. If the total amount of the additive is less than 0.1 part by weight, the effect of the additive may not be sufficiently exhibited. If the additive is more than 5 parts by weight, the amount of the conductive powder may be reduced.

The paste composition may further comprise glass or crystalline inorganic material in addition to the above-described conductive powder, glass frit, and organic vehicle. Such a glass or crystalline inorganic material may be added to improve the thermal characteristics, the baking characteristics, the adhesive force, and the sintering property, the compactness, etc. of the conductive powder of the paste composition. For example, lead oxide (PbO) -based glass may be used as the glass, and lead oxide, boron oxide, zinc oxide, and the like may be further included as the crystalline inorganic material. Various other known materials may be used. Such a separate glass or crystalline inorganic material may be included in an amount of 0.01 to 5 parts by weight, based on 100 parts by weight of the total paste composition. If the weight part is less than 0.01 total, the effect may not be sufficient. If the weight part is more than 5 in total, the content of other materials constituting the conductive paste may be decreased and the characteristics may be lowered. However, the present invention is not limited thereto, and the content of the free glass or crystalline inorganic material may be variously modified.

Such a paste composition can be prepared by the following method.

The binder is dissolved in a solvent and then pre-mixed to form an organic vehicle. The conductive powder, glass frit and additives are added to the organic vehicle and aged for a period of time. The aged mixture is mechanically mixed and dispersed through a 3 roll mill or the like. The mixture is filtered and defoamed to prepare a paste composition. However, this method is merely an example, and the present invention is not limited thereto.

The paste composition thus prepared is coated on the antireflection film 22 by various methods (for example, screen printing or the like) on the semiconductor substrate 110 and then fired to connect it to the emitter region 20 by the fire- The first electrode 24 is formed.

The paste composition according to the present embodiment is characterized in that the glass frit contains lead oxide and thallium oxide. As a result, the lead oxide can smoothly fire through, and the contact characteristics between the first electrode 24 and the semiconductor substrate 110 or the emitter region 20 can be maintained at a good level. And the content of lead oxide including thallium oxide can be reduced, and the glass stability at low temperature can be improved while lowering the glass transition temperature of the glass frit. Accordingly, the contact characteristics of the first electrode 24 and the emitter region 20 can be uniformly realized even when the firing is performed at a low temperature.

In particular, when the n-type base region 10 and the p-type emitter region 20 are provided, the firing temperature of the first electrode 24 may be low. Therefore, If the first electrode 24 connected to the region 20 is used, the effect can be doubled.

However, the present invention is not limited thereto, and the paste composition according to this embodiment can be used for the first electrode 24 connected to the n-type emitter region 20. [ In the above description, the paste composition according to this embodiment is applied to the first electrode 24 connected to the emitter region 20, but the present invention is not limited thereto. Therefore, the paste composition according to the present embodiment may be applied to the second electrode 34 connected to the rear electric field area 30 by etching and pass through the passivation film 32, and various other modifications are possible Do.

In another embodiment, a paste composition comprising a thallium compound (particularly thallium oxide) as a separate additive from glass frit is described in detail.

The description of the above-mentioned embodiments is made for the description of additives other than thallium compounds added with glass frit as a separate additive, conductive powder, organic vehicle, additive such as dispersant, shaving agent, etc., and glass or crystalline mineral added separately Can be applied as it is.

In this embodiment, the glass frit may have the same composition as the glass frit in the above embodiment. Alternatively, glass frit of various known compositions different from the above-described embodiment may be used. That is, the glass frit in the present embodiment is not particularly limited and may include various compositions.

As the thallium compound, thallium oxide may be applied to maximize the stabilizing effect in the free state, and various compounds other than thallium oxide (for example, thallium nitride, thallium fluoride, thallium carbide, etc.) may be applied.

The paste composition according to this embodiment contains 0.01 to 5 parts by weight of thallium oxide per 100 parts by weight of the total. The thallium oxide thus contained can serve to lower the glass transition temperature of the glass frit in the paste composition and to improve the glass stability. If the thallium oxide is less than 0.01 part by weight, the effect of thallium oxide may not be sufficient. If the amount of the thallium oxide is more than 5 parts by weight, the content of other materials or the like of the paste composition may be reduced to deteriorate the characteristics of the paste composition and the electrode produced thereby.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited thereto.

Example  One

After mixing 80 mol% of lead oxide (PbO), 10 mol% of thallium oxide (Tl ₂ O), 5 mol% of silicon oxide (SiO ₂ ) and 5 mol% of boron oxide (B ₂ O ₃ ) ° C, dropped into droplets, and passed between two rolls to obtain a plate-like shape, which was then pulverized to prepare a glass frit having a center particle diameter of 1 um.

An organic vehicle was prepared by dissolving 0.5 parts by weight of ethylcellulose-based binder in 8 parts by weight of butylcarbitol (solvent), based on 100 parts by weight of the whole. To the organic vehicle, 86 parts by weight of silver powder (conductive powder), 3.5 parts by weight of the glass frit and 2 parts by weight of dispersant were added and mixed. This was aged for 12 hours and then mixed and dispersed in a second roll using a three roll mill. This was filtered and defoamed to prepare a paste composition.

Example  2

Except that 70 mol% of lead oxide, 20 mol% of thallium oxide, 5 mol% of silicon oxide, and 5 mol% of boron oxide were used in the production of glass frit, . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Example  3

Except that 60 mol% of lead oxide, 30 mol% of thallium oxide, 5 mol% of silicon oxide, and 5 mol% of boron oxide were used in the production of the glass frit. . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Example  4

A glass frit was produced in the same manner as in Example 1, except that 50 mol% of lead oxide, 40 mol% of thallium oxide, 5 mol% of silicon oxide, and 5 mol% . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Example  5

Except that 30 mol% of lead oxide, 60 mol% of thallium oxide, 5 mol% of silicon oxide, and 5 mol% of boron oxide were used in the preparation of the glass frit. . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  One

Except that 89.5 mol% of lead oxide, 0.5 mol% of thallium oxide, 5 mol% of silicon oxide and 5 mol% of boron oxide were used in the production of glass frit, . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  2

A glass frit was prepared in the same manner as in Example 1, except that 5 mol% of lead oxide and 95 mol% of thallium oxide were used in the production of the glass frit and no silicon oxide and boron oxide were used. A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  3

Except that 80 mol% of lead oxide, 10 mol% of thallium oxide, 5 mol% of silicon oxide, and 5 mol% of boron oxide were used in the preparation of the glass frit. . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  4

Except that 89.5 mol% of lead oxide, 8 mol% of silicon oxide, 2 mol% of aluminum oxide (Al ₂ O ₃ ) and 0.5 mol% of copper oxide (CuO) were used in the production of glass frit A glass frit was prepared in the same manner as in Example 1. A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  5

Except that 79.5 mol% of lead oxide, 18 mol% of silicon oxide, 2 mol% of aluminum oxide and 0.5 mol% of copper oxide were used in the production of glass frit, . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  6

Except that 69.5 mol% of lead oxide, 28 mol% of silicon oxide, 2 mol% of aluminum oxide and 0.5 mol% of copper oxide were used in the production of the glass frit. . A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  7

Except that 88.8 mol% of lead oxide, 8 mol% of silicon oxide, 2 mol% of aluminum oxide, 0.2 mol% of copper oxide and 1 mol% of lithium oxide (Li ₂ O) were used in the production of glass frit The glass frit was prepared in the same manner as in Example 1. A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  8

Except that 88.8 mol% of lead oxide, 8 mol% of silicon oxide, 2 mol% of aluminum oxide, 0.2 mol% of copper oxide and 1 mol% of sodium oxide (Na ₂ O) were used in the production of glass frit The glass frit was prepared in the same manner as in Example 1. A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

Comparative Example  9

Example 1 was repeated except that 79.5 mol% of lead oxide, 10 mol% of bismuth oxide, 8 mol% of silicon oxide, 2 mol% of aluminum oxide and 0.5 mol% of copper oxide were used in the production of glass frit To prepare a glass frit. A paste composition was prepared in the same manner as in Example 1 using the glass frit thus prepared.

The paste compositions according to Examples 1 to 5 and Comparative Examples 1 to 9 were applied on a nitride film formed on a semiconductor substrate by printing and then fired to determine the etching characteristics of the nitride film of the glass frit composition. Then, the contact resistances of the electrode and the semiconductor substrate formed by baking the paste composition according to Examples 1 to 5 and Comparative Examples 1 to 9 on a semiconductor substrate were measured. At this time, the contact resistance was measured by a measuring instrument of DENKEN.

The results of the above-mentioned measurements and judgments are shown in Table 1.

Composition of glass frit (mol%) Etching characteristics Contact resistance
[ohm] Remarks Example 1 PbO (80), Tl ₂ O (10),
SiO ₂ (5), B ₂ O ₃ (5) Great 4.1 Example 2 PbO (70), Tl ₂ O (20),
SiO ₂ (5), B ₂ O ₃ (5) Great 4.4 Example 3 PbO (60), Tl ₂ O (30),
SiO ₂ (5), B ₂ O ₃ (5) Great 5.1 Example 4 PbO (50), Tl ₂ O (40),
SiO ₂ (5), B ₂ O ₃ (5) Great 5.8 Example 5 PbO (30), Tl ₂ O (60),
SiO ₂ (5), B ₂ O ₃ (5) usually 6.0 Comparative Example 1 PbO (99.5), Tl ₂ O (0.5) - - crystallization
(Difficult to vitrify) Comparative Example 2 PbO (5), Tl ₂ O (95) Bad
(Contact not available) - Comparative Example 3 _{PbO (79.5), Bi 2 O} 3 (10),
SiO ₂ (5), B ₂ O ₃ (5) Great 8.2 Comparative Example 4 _{PbO (89.5), SiO 2 (} 8), Al 2 O 3 (2), CuO (0.5) Great 5.6 Comparative Example 5 _{PbO (79.5), SiO 2 (} 18), Al 2 O 3 (2), CuO (0.5) Great 7.9 Comparative Example 6 _{PbO (69.5), SiO 2 (} 28), Al 2 O 3 (2), CuO (0.5) Great 8.3 Comparative Example 7 _{PbO (88.8), SiO 2 (} 8), Al 2 O 3 (2), CuO (0.5), Li 2 O (1) Great 6.1 Comparative Example 8 _{PbO (88.8), SiO 2 (} 8), Al 2 O 3 (2), CuO (0.5), Na 2 O (1) Great 6.4 Comparative Example 9 _{PbO (79.5), Bi 2 O} 3 (10),
SiO ₂ (8), Al ₂ O ₃ (2), CuO (0.5) Great 6.3

Referring to Table 1, the glass frit according to Examples 1 to 5 can be sufficiently etched by the lead oxide to sufficiently etch the nitride film. In this case, in Example 5, in which the mol% of lead oxide is relatively small, the etching characteristics may be somewhat lowered than in Examples 1 to 4, in which the etching characteristics are normal and the etching characteristics are excellent. Accordingly, in consideration of the etching characteristics, the lead oxide may be contained in an amount of 50 mol% or more, and the lead oxide may be contained in an amount of 60 mol% or more for more stable etching characteristics in consideration of the process margin and the like.

In Examples 1 to 5, the lead oxide and thallium oxide have a low glass transition temperature and are sufficiently vitrified at the firing temperature, so that the electrode can be contacted with a uniform and excellent property on the semiconductor substrate. At this time, in Examples 1 to 4 in which thallium oxide is contained in an amount of 10 mol% to 40 mol%, the resistance value may be as low as 6.0 ohms or less. In particular, in Examples 1 and 3, in which thallium oxide was contained in an amount of 10 mol% to 30 mol%, the resistance value was as low as 5.1 ohm or less, and in Examples 1 and 2 in which thallium oxide was contained in an amount of 10 mol% to 20 mol% It can be seen that the resistance value is very low as 4.1 and 4.4. This is presumably because the glass stabilization effect by the thallium oxide and the etching effect by the lead oxide are sufficiently exhibited.

On the other hand, in Comparative Example 1 in which lead oxide is contained in an amount of 99.5 mol%, many crystallization occurs and it is difficult to vitrify the glass frit. In Comparative Example 2 in which the lead oxide is contained in an amount of less than 5 mol%, the etching property is very poor, and the nitride remains as it is, and it is found that the electrical connection between the electrode and the semiconductor substrate is difficult.

In Comparative Examples 3 to 9 in which thallium oxide is not used, the resistance is higher than in Examples 1 to 5. In particular, it can be seen that Comparative Example 3 using bismuth oxide instead of thallium in the composition of Example 1 has a very high resistance. It is expected that the use of bismuth oxide can lower the glass transition temperature, but the glass stability is lowered and the sintering property of the silver powder by the glass is lowered. Comparative Examples 4 to 9 were obtained by optimizing the composition of the glass frit in order to improve the glass stability, and generally had a lower contact resistance than Comparative Example 3, but higher resistance than Examples 1 to 5.

Example  6

An organic vehicle was prepared by dissolving 0.5 parts by weight of an ethylcellulose-based binder in 8 parts by weight of butylcarbitol (solvent), based on 100 parts by weight of the entire paste composition. 84 parts by weight of silver powder (conductive powder), 3.5 parts by weight of glass frit according to Comparative Example 7, 2 parts by weight of dispersant, and 2 parts by weight of thallium oxide were added to the organic vehicle and mixed to prepare a paste composition .

Comparative Example  10

An organic vehicle was prepared by dissolving 0.5 parts by weight of an ethylcellulose-based binder in 8 parts by weight of butylcarbitol (solvent), based on 100 parts by weight of the entire paste composition. To the organic vehicle, a paste composition was prepared by adding 85.95 parts by weight of silver powder (conductive powder), 3.5 parts by weight of glass frit according to Comparative Example 7, 2 parts by weight of dispersant, and 0.05 part by weight of thallium oxide .

Comparative Example  11

An organic vehicle was prepared by dissolving 0.5 parts by weight of an ethylcellulose-based binder in 8 parts by weight of butylcarbitol (solvent), based on 100 parts by weight of the entire paste composition. To the organic vehicle, a paste composition was prepared by adding 76 parts by weight of silver powder (conductive powder), 3.5 parts by weight of glass frit according to Comparative Example 7, 2 parts by weight of dispersant, and 10 parts by weight of thallium oxide, .

The paste composition according to Example 6 and Comparative Examples 10 and 11 was applied onto a semiconductor substrate and then fired to measure the contact resistance between the electrode and the semiconductor substrate.

The results of the above measurement and judgment are shown in Table 2 together with the results of Comparative Example 7.

Etching characteristics Contact Resistance [ohms] Example 6 Great 5.2 Comparative Example 7 Great 6.1 Comparative Example 10 Great 6.0 Comparative Example 11 Great 6.8

Referring to Table 2, it can be seen that Example 6 in which thallium oxide is added separately from glass frit has lower contact resistance than Comparative Example 7 in which thallium oxide is not added separately from glass frit. This is presumably because glass stability of the glass frit is improved by adding thallium oxide to the paste composition. However, when the amount of thallium oxide is too small as in Comparative Example 10, the effect of improving the glass stability of glass frit due to thallium oxide is hardly observed. When the amount of thallium oxide is too large as in Comparative Example 11, The content of the powder may be reduced and the resistance may be increased.

Features, structures, effects, and the like according to the above-described embodiments are included in at least one embodiment of the present invention, and the present invention is not limited to only one embodiment. Further, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

150: Solar cell
110: semiconductor substrate
10: Base area
20: Emitter area
30: Rear field area
22: Antireflection film
32: Passivation film
24: first electrode
34: Second electrode

Claims (18)

1. A paste composition for a solar cell electrode for use in a solar cell electrode,
A paste composition for a solar cell electrode comprising a thallium compound. The method according to claim 1,
Wherein the paste composition for a solar cell electrode comprises a thallium oxide. 3. The method of claim 2,
Wherein the paste composition comprises a conductive powder, a glass frit and an organic vehicle,
Wherein the glass frit comprises a lead oxide and the thallium oxide. The method of claim 3,
Wherein the thallium oxide is contained in an amount of 1 to 90 mol% based on 100 mol% of the total glass frit. 5. The method of claim 4,
Wherein the thallium oxide is contained in an amount of 1 to 50 mol% based on 100 mol% of the total glass frit. 6. The method of claim 5,
Wherein the thallium oxide is contained in an amount of 10 to 40 mol% based on 100 mol% of the entire glass frit. The method of claim 3,
Wherein the glass frit is made of the lead oxide and the thallium oxide,
Wherein the thallium oxide is contained in an amount of 1 to 90 mol% based on 100 mol% of the entire glass frit, and the lead oxide is contained in an amount of 10 to 99 mol%. The method of claim 3,
Wherein the glass frit further comprises a glass frit material other than the lead oxide and the thallium oxide. 9. The method of claim 8,
Wherein the other glass frit material comprises at least one of silicon oxide, barium oxide, phosphorus oxide, lithium oxide, sodium oxide, potassium oxide, zinc oxide and aluminum oxide. 9. The method of claim 8,
Wherein the sum of the lead oxide and the thallium oxide is 50 mol% or more based on 100 mol% of the total glass frit. 9. The method of claim 8,
Wherein the total amount of the other glass frit material is from 1 to 50 mol% based on 100 mol% of the total glass frit. The method according to claim 1,
Wherein the glass frit composition has a glass transition temperature of 200 to 400 占 폚. 13. The method of claim 12,
Wherein the glass frit composition has a glass transition temperature of 200 to 300 占 폚. 3. The method of claim 2,
Wherein the paste composition comprises a conductive powder, a glass frit and an organic vehicle,
Wherein the thallium oxide is contained in the paste composition separately from the glass frit. 15. The method of claim 14,
Wherein the paste composition contains 0.01 to 5 parts by weight of thallium oxide per 100 parts by weight of the total paste composition. A photoelectric conversion unit; And
The electrode connected to the photoelectric conversion unit
/ RTI >
Wherein the electrode comprises lead and thallium. 17. The method of claim 16,
Wherein the photoelectric conversion unit comprises:
A semiconductor substrate; And
The emitter region formed in the semiconductor substrate
/ RTI >
And the electrode is a front electrode electrically connected to the emitter region. 18. The method of claim 17,
Wherein the emitter region has a p-type.

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