阅读说明：本技术 一种太阳能电池导电浆料、玻璃料及太阳能电池 (Solar cell conductive paste, glass material and solar cell ) 是由 敖毅伟 万莉 涂小平 姜钧天 朱立波 刘海东 于 2020-04-08 设计创作，主要内容包括：本发明公开了一种太阳能电池导电浆料,含有导电性粉末、混合玻璃以及有机相；其中,所述混合玻璃包含以下两类玻璃组分：第一类玻璃是选自不含铅锌硅,以碲铋锂为必需成分的碲系玻璃的至少一种；第二类玻璃是选自以铅硅钒为必需成分,不含碲铋的硅酸铅系玻璃的至少一种。本发明还提供了一种玻璃料及太阳能电池。利用本发明的导电浆料制得的太阳能电池的EL检测正常,电池效率高,而且粘结强度优良。(The invention discloses a solar cell conductive paste, which contains conductive powder, mixed glass and an organic phase; wherein the mixed glass comprises the following two glass components: the first glass is at least one selected from tellurium series glass which does not contain lead, zinc and silicon and takes tellurium, bismuth and lithium as essential components; the second glass is at least one selected from lead silicate glasses containing lead, silicon and vanadium as essential components and no bismuth telluride. The invention also provides the glass material and a solar cell. The solar cell prepared by the conductive paste has normal EL detection, high cell efficiency and excellent bonding strength.)

1. The solar cell conductive paste is characterized by comprising conductive powder, mixed glass and an organic phase; wherein the mixed glass comprises the following two glass components: the first glass is at least one selected from tellurium series glass which does not contain lead, zinc and silicon and takes tellurium, bismuth and lithium as essential components; the second glass is at least one selected from lead silicate glasses containing lead, silicon and vanadium as essential components and no bismuth telluride.

2. The electroconductive paste according to claim 1, wherein in the mixed glass, the mass ratio of the total amount of the tellurium-based glass to the total amount of the lead silicate-based glass is 3: 7-7: 3.

3. the electroconductive paste according to claim 1 or 2, wherein the tellurium-based glass is, in terms of oxide, 50 to 90 wt% of tellurium, 8 to 40 wt% of bismuth, and 2 to 15 wt% of lithium.

4. The electroconductive paste according to claim 1 or 2, wherein said lead silicate-based glass has 25 to 80 wt% of lead, 1 to 50 wt% of silicon, and 10 to 40 wt% of vanadium, in terms of oxide.

5. The electroconductive paste according to claim 4, wherein the lead silicate-based glass contains 40 to 70 wt% of lead and 5 to 20 wt% of silicon.

6. The conductive paste according to claim 1 or 2, wherein the lead silicate-based glass further comprises one or any of zinc, tungsten, sodium, lithium, aluminum, copper, magnesium.

7. The conductive paste according to claim 5, wherein the total of tungsten, sodium, lithium, aluminum, copper, and magnesium is 0 to 20 wt%.

8. The electroconductive paste according to claim 1 or 2, wherein the content of the mixed glass is controlled to be 0.5 to 8 by mass for the electroconductive powder of 100 by mass.

9. A frit comprising the hybrid glass as defined in any one of claims 1 to 8.

10. A solar cell prepared from the electroconductive paste according to any one of claims 1 to 8.

Technical Field

The invention belongs to the technical field of solar cell slurry, and particularly relates to preparation of Te-Bi-Li lead-free zinc-silicon glass frit and Pb-V-Si tellurium-bismuth-free glass frit, and conductive slurry prepared from the two glass frits.

Background

A conventional silicon crystal solar cell is composed of a front surface electrode, an antireflection film, a P-type silicon crystal semiconductor substrate, an N-type diffusion layer, a back surface electrode, and the like. With the continuous progress of the battery technology, a passivation layer is added on the semi-conductive diffusion layer for improving the efficiency, wherein the passivation layer is generally made of aluminum oxide, silicon oxide and the like, and the antireflection film is generally made of silicon nitride. In addition, the appeal of the battery plate manufacturer to the efficiency enables the diffusion square resistance of the silicon wafer to be continuously improved, and the PN junction is changed from deep to shallow.

As a binder phase of the electrode paste, the properties of the glass frit directly determine the bonding strength and contact resistance after the paste is sintered. The glass phase systems currently commercialized are mainly of two types, the first being the Pb/Bi-Si system and the second being the Te-Pb/Bi-Si system. The first glass system is easy to burn through PN junction and cannot meet the contact of a high-sheet-resistance silicon wafer, the second glass system reduces the bonding strength between an electrode and a substrate along with the increase of PbO content, and the influence on the bonding strength can be considered to be related to the shape of a substrate/electrode interface. That is, if PbO is contained in the glass, it does not contain hard SiO₂The glass also corrodes the substrate and good contact between the substrate and the electrode is formed. However, if the composition of PbO is excessive, the substrate is etched more uniformly, and the etched surface becomes smoother, resulting in a decrease in the bonding strength.

The most effective scheme at present is to use tellurium series glass according to the requirements of the bonding strength and the contact resistance of the solar cell electrode. The tellurium in the glass component is used as a network forming body, can increase the dissolution amount of silver in the glass, reduce the contact resistance, and can inhibit the precipitation of the silver in the sintering temperature reduction section, thereby widening the sintering window and simultaneously inhibiting the semiconductor substrate from being excessively corroded. Therefore, the development of lead-free tellurium-based glasses is a current research focus.

In many studies, it has been found that the use of a paste for a lead-free tellurium-based glass electrode is characterized in that the adhesive strength can be achieved by adjusting the softening point of the glass, but the lead-free glass is more difficult to control the degree of corrosion than the lead glass, and good contact conditions can be achieved. In the EL test, sintering problems such as black spots or cloud-like black spots often occur, which affect the performance of the solar cell, and referring to fig. 1, several cases of poor EL test are shown.

In addition, researchers have found that the softening point of the Pb-Bi-Si glass system is relatively high, the ball milling time during the preparation process is long and the particle size is large, resulting in poor wettability. The softening temperature of the glass powder is an important index for measuring the performance of the glass powder, if the softening point is lower than 400 ℃, the glass powder can prematurely start flowing in the high-temperature sintering process, and the PN junction is easily broken down; and when the softening point temperature is higher than 600 ℃, the glass powder is not easy to melt in the high-temperature sintering process, so that the glass powder cannot react with the antireflection film and penetrate through the antireflection film to contact with the silicon wafer during sintering. The glass has low softening point, so that the wettability to silver powder and a substrate is good, and the wettability is strong, so that the antireflection film can be corroded, the contact resistance is reduced, and the battery performance is improved. Thus, the softening point of the frit will be directly related to the electrical properties and the sintering window.

Based on the above consideration, it is necessary to develop an electrode paste which is qualified in EL detection, has good electrical properties, and has good bonding strength.

Disclosure of Invention

The invention provides a solar cell conductive paste in a first aspect, which can solve the above defects in the prior art.

The technical scheme of the invention is as follows:

a solar cell conductive paste comprises conductive powder, mixed glass and an organic phase; wherein the mixed glass comprises the following two glass components: the first glass is at least one selected from tellurium series glass which does not contain lead, zinc and silicon and takes tellurium, bismuth and lithium as essential components; the second glass is at least one selected from lead silicate glasses containing lead, silicon and vanadium as essential components and no bismuth telluride.

Preferably, in the mixed glass, the mass ratio of the total amount of the tellurium series glass to the total amount of the lead silicate series glass is 3: 7-7: 3.

preferably, the tellurium series glass is converted into oxide, tellurium accounts for 50-90 wt%, bismuth accounts for 8-40 wt%, and lithium accounts for 2-15 wt%.

In some embodiments, the tellurium-based glass may further contain at least one of oxides of tungsten and lithium.

Preferably, the lead silicate-based glass contains 25 to 80 wt% of lead, 1 to 50 wt% of silicon, and 10 to 40 wt% of vanadium, in terms of oxide.

Preferably, in the lead silicate glass, the content of lead is 40 to 70 wt%, and the content of silicon is 5 to 20 wt%.

Preferably, the lead silicate glass further comprises one or any of zinc, tungsten, sodium, lithium, aluminum, copper and magnesium.

Preferably, the total of tungsten, sodium, lithium, aluminum, copper and magnesium is 0 to 20 wt%.

Preferably, the content of the mixed glass is controlled to be 0.5 to 8 by mass for the conductive powder of 100 by mass.

Preferably, the mixed glass further contains another glass, and the total amount by mass of the first glass and the second glass is more than 50% with respect to 100% by mass of the mixed glass.

The second aspect of the present invention also provides a frit comprising a hybrid glass as described in any of the above.

The third aspect of the invention also provides a solar cell prepared from any one of the conductive pastes.

Compared with the prior art, the invention has the following beneficial effects:

the solar cell prepared by the conductive paste has normal EL detection, high cell efficiency and excellent bonding strength.

Of course, it is not necessary for any product that implements the invention to achieve all of the above-described advantages at the same time.

Drawings

FIG. 1 is a graph showing the results of EL tests on pastes Nos. 1 to 11 of example 2 of the present invention;

FIG. 2 is a graph showing the results of EL test of pastes Nos. 12 to 23 of example 2 of the present invention.

Detailed Description

The invention provides two kinds of glass powder and conductive paste for a solar cell prepared by using the two kinds of glass powder.

The applicant researches the existing lead-free tellurium series glass, and thinks that the bismuth component in the lead-free tellurium series glass can properly weaken the stronger corrosion inhibition effect of tellurium, thereby improving the corrosion resistance of the lead-free tellurium series glass, but the bismuth-containing lead-free tellurium series glass is easy to phase split and crystallize in the preparation process, is not easy to form glass, and affects the stability of glass preparation. This also causes the high-fluidity portion and the low-fluidity portion of the electrode to separate during the high-temperature sintering, and non-uniform ohmic contact is formed between the semiconductor substrate and the electrode paste, and poor sintering problems such as a fulcrum and cloud can be found by the EL inspection. The occurrence of the problem puts new requirements on the conductive paste, and the development of the electrode paste which is qualified in EL detection, good in electrical property and high in bonding strength is needed.

Aiming at the problem, the invention provides the electrode paste which can ensure the electrical property and the bonding strength and is qualified in EL detection.

In order to achieve the above object, the present inventors have conducted extensive studies and finally confirmed the following three points: first, aiming at the problems that the bismuth-containing lead-free tellurium series glass is easy to phase split and not easy to form glass in the preparation process, and the preparation stability of the glass is influenced, if zinc and silicon are removed in a formula system, a glass forming window can be widened well, the yield is high, and the stability is good. Secondly, aiming at the problems that the softening point of a lead bismuth silicate glass system is relatively high, the ball milling time is long and the particle size is large in the preparation process, so that the wettability is poor, vanadium oxide can be used for replacing bismuth oxide; the vanadium oxide can obviously reduce the melting point and the softening temperature of the glass, enlarge the forming temperature range of the glass, shorten the ball milling time and meet the requirement on the particle size distribution. Thirdly, the two glasses are mixed for use, the electrode slurry has no poor EL phenomenon after sintering, and simultaneously, the electrical property and the bonding strength are considered.

The proposal of the invention is based on the above discovery of the inventor. The conductive paste according to the present invention is a conductive paste for forming a solar cell electrode, and is characterized by using at least a conductive powder, and simultaneously using a tellurium-based glass containing bismuth lithium telluride as a main component and substantially no lead, zinc and silicon, and a lead silicate-based glass containing lead, silicon and vanadium telluride as a main component and substantially no bismuth telluride.

The conductive paste as described above, wherein the first glass may comprise one or more tellurium-based glasses substantially free of lead, silicon, zinc and bismuth lithium telluride as essential components; the second type of glass may comprise one or more lead silicate-based glasses that contain lead, silicon, vanadium as an essential component and are substantially free of bismuth telluride. In the following detailed tables, if the specific constituent components of each element of each glass are not described, the element is contained as an oxide in the glass.

The conductive paste contains the above-described conductive powder, mixed glass, an appropriate amount of additives, and an organic phase. The conductive paste may be a rheological paste, a paint, or an ink-like composition suitable for printing methods other than screen printing.

The content of the mixed glass in the conductive paste can be referred to the amount generally used in the conductive paste for a solar cell electrode. However, in this case, for example, it is preferable that the content of the mixed glass is controlled to about 0.5 to 8 by mass for the conductive powder having a mass of 100, and if the content of the mixed glass is 0.5 or more, predetermined sealing property and electrode strength can be obtained; if the quality of the mixed glass is 8 or less, the electrode surface floats out of the glass, and the increase in contact resistance can be helped to be reduced by the interface glass flowing into the electrode and the diffusion layer of the semiconductor substrate. Although not particularly limited, the tellurium-based glass and the lead silicate-based glass in the conductive paste of the present embodiment preferably have an average particle size of 0.4 to 4.0 μm.

The conductive powder is not limited except for the requirement that the main component is silver, and the shape thereof may be spherical, flaky, dendritic, or the like. In addition to the pure silver powder, a silver-coated composite powder having a silver layer at least on the surface, an alloy mainly composed of silver, or the like may be used. The average particle diameter of the conductive powder such as silver powder is preferably 0.1 to 10 μm. Two or more kinds of conductive powders having different average particle diameters, particle size distributions, shapes, and the like may be mixed and used, and even a silver powder and a conductive powder other than silver may be mixed and used together. The above-mentioned "main component" means a component exceeding 50% by mass, preferably 70% by mass. In addition, the metal compounded, alloyed or mixed with the silver powder is not limited as long as the effect of the present invention and the embodiment thereof is not impaired, and examples thereof include aluminum, gold, palladium, copper, nickel and the like. However, silver powder is most recommended from the viewpoint of conductivity.

There is also no particular restriction on the organic phase, and silver paste is generally used rationally. Organic resins and organic solvents generally used in organic phases. In addition, as the organic resin, cellulose, acrylic resins, phenol resins, alkyd resins, rosin resins, or the like can be used. As the organic solvent, an organic solvent such as alcohols, ethers, esters, hydrocarbons, etc., or water, or a mixed solvent thereof can be used. Therefore, the ratio of the organic phase is not particularly limited, and an appropriate amount of the organic phase may be used to form a slurry with inorganic components such as conductive powder and mixed glass, and the slurry may be appropriately adjusted by a method such as coating. In general, the mass of the organic phase is about 5 to 40 for a conductive powder having a mass of 100.

If necessary, an appropriate amount of a conventionally used additive such as a plasticizer, a viscosity modifier, an interfacial active agent, an oxidizing agent, a metal oxide, a metal organic compound, or the like may be added to the other components within a range not to impair the action and effects of the present invention and the embodiments thereof. In addition, a silver compound such as silver carbonate, silver oxide, or silver acetate may be used, and copper oxide, zinc oxide, tungsten oxide, or titanium oxide may be added in an appropriate amount in order to optimize the sintering temperature and improve the characteristics of the solar cell.

In the tellurium-based glass of the present invention, tellurium content is 50 to 90 wt%, bismuth content is 8 to 40 wt%, and lithium content is 2 to 15 wt%, in terms of oxide. Tellurium plays a role of a network former, can increase the dissolution amount of silver in glass, reduce contact resistance, can inhibit the precipitation of silver in a sintering cooling section, widens a sintering window and simultaneously has the function of inhibiting the corrosion to a semiconductor substrate. By these actions, the insulating film can be sufficiently etched to ensure good contact between the electrode material and the substrate, and the electrode material entering the semiconductor layer region such as a PN junction can be suppressed, whereby good ohmic contact can be more easily formed, and further, the conductivity can be improved and the electrical properties can be improved. In addition, burn-through control is also easier, which is also helpful for thinning the semiconductor layer on the light-receiving surface side. If the content of tellurium is less than 40 wt%, the amount of silver dissolved in the glass cannot be sufficiently increased, and if it exceeds 90 wt%, the effect of suppressing corrosion becomes too strong, and thus burn-through cannot be sufficiently achieved.

Bismuth is a component for increasing the softening point of the glass, and this component can be added when the softening point of the tellurium-based glass is adjusted while ensuring low viscosity thereof, and can impart a corrosive action to the glass. Although tellurium has a strong corrosion inhibiting effect, the corrosion can be controlled to an adequate level by appropriately adjusting the bismuth content, but if the bismuth content exceeds 50 wt%, the glass is easily crystallized.

In the case of an N-type semiconductor, the donor concentration near the interface is lowered by interdiffusion between the semiconductor substrate and the electrode material, and lithium can be supplied. If the content of lithium is less than 2 wt%, it cannot be sufficiently supplemented, but if it exceeds 15 wt%, the corrosion is too strong and the glass stability is deteriorated. In general, the alkali metal component has an adverse effect on the solar cell characteristics, and therefore, it is not preferable to use it. For example, Na causes a decrease in the open voltage Voc, K causes a decrease in FF and increases the contact resistance, and Na and K do not form donors and are therefore not useful. Lithium is useful because lithium has a replenishing effect and can provide superior solar cell characteristics in the formation of an electrode of an N-type semiconductor.

The lead silicate glass contains lead, silicon and vanadium as essential components, and may further contain one or more of zinc, tungsten, sodium, lithium, aluminum, copper and magnesium. The element is converted into oxide, lead accounts for 25-80 wt%, vanadium accounts for 10-40 wt%, silicon accounts for 5-20 wt%, and tungsten, sodium, lithium, aluminum, copper and magnesium account for 0-20 wt%. More preferably, the lead content is preferably between 40 and 60 wt%.

Lead is mainly used as a network former for forming a network of the lead silicate-based glass, and has a glass forming ability alone, and the content is preferably 40 to 60 wt%, and in this range, the burn-through property is improved.

Silicon, especially in the above lead silicate based glasses, can help to form a glass network, making it easier to adjust the softening point. When the content is 1 to 50 wt% in terms of silica, glass formation is more likely, and the content is preferably in the range of 5 to 20 wt%. When the content exceeds 50 wt%, the softening point becomes too high and the lead is a network-forming component, which may inhibit the formation of the network.

The vanadium oxide can obviously reduce the melting point and the softening temperature of the glass, expand the forming temperature range of the glass, simultaneously shorten the ball milling time and meet the requirement of the particle size distribution, and the content is preferably 10 to 40 weight percent.

The above lead silicate glass may further contain one or more of zinc, tungsten, sodium, lithium, aluminum, copper and magnesium, and the total amount of these elements is preferably 20 wt% or less in terms of oxides.

In order to obtain a good appearance and a high-stability surface electrode in the EL test, it is preferable to control the mass ratio of the tellurium-based glass to the lead silicate-based glass in the mixed glass to 3: 7-7: 3. the glass mixture may contain at least tellurium glass and lead silicate glass, and may further contain other glass without substantially affecting the effect of the present invention, and preferably the total amount of the tellurium glass and the lead silicate glass is more than 50% by mass with respect to 100% by mass of the glass mixture.

As described above, when the conductive paste is made of a mixed glass mainly composed of a tellurium-based glass containing no lead-silicon-zinc and containing no bismuth-lithium telluride as essential components and a lead silicate-based glass containing no lead-silicon-vanadium and containing no bismuth-tellurium, good balance between the ohmic contact and the adhesive strength can be achieved, and the EL test can be passed. The effect cannot be achieved by using tellurium series glass alone or lead silicate series glass alone, and the effect cannot be achieved by using lead tellurium series glass alone.

In this context, a range of values from one value to another is a general expression avoiding any recitation of all values in the range in the specification. Thus, recitation of a range of values herein is intended to encompass any value within the range and any smaller range of values encompassed within the range, as if the range and any smaller range of values were explicitly recited in the specification.

The conductive paste of the present invention will be described in detail with reference to specific examples. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. In practice, the invention will be understood to cover all modifications and variations of this invention provided they come within the scope of the appended claims.