JP2008010527A - Conductive paste for solar cell electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste for solar cell electrode, with which high FF can stably be obtained, especially conductive paste for forming an electrode on an n-type semiconductor of a crystal system silicon solar cell. <P>SOLUTION: Conductive paste for solar cell electrode comprises organic binder, solvent, conductive particles, glass frit and Sn compound. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conductive paste for a solar cell electrode, in particular, a conductive paste for forming an electrode on an N-type semiconductor of a crystalline silicon solar cell, a solar cell electrode formed by firing the conductive paste, and the electrode And a method for producing a solar cell using the conductive paste.

  Conventional solar cells using single crystal or polycrystalline silicon as the main semiconductor substrate material are electrons / holes generated by light incident / absorbed in the semiconductor due to the electric field generated at the PN junction provided near the substrate surface. The pair is separated and taken out to the outside as an electric current through an electrode formed to have a low contact resistance with each of the P-type semiconductor and the N-type semiconductor.

  For example, in the case of a general polycrystalline silicon solar cell, an element capable of forming an N-type diffusion layer such as P (phosphorus atom) from one side surface of a P-type silicon substrate doped with B (boron atom) or the like as an impurity. Diffusion to form a PN junction. In this case, in order to have a light confinement effect, the N-type diffusion layer is formed after texture (unevenness) processing is performed on the surface of the P-type silicon substrate.

  A light incident side electrode composed of a bus electrode and a finger electrode is formed through an antireflection film (film thickness: 50 to 100 nm) such as silicon nitride and titanium oxide with the N-type diffusion layer side as a light incident side. Since light does not need to be incident on the P-type silicon substrate side on the back side, the back side electrode is formed on almost the entire surface. Both electrodes need to be in ohmic contact with each semiconductor with low resistance.

  Both electrodes are generally formed by printing, drying and firing a conductive paste. The conductive paste composition and firing conditions are particularly important for the characteristics of the solar cell.

  The conductive paste generally contains an organic binder, a solvent, conductive particles, and glass frit, and an additive is optionally blended. These components include control of printability and shape after printing, imparting conductivity as an electrode, maintaining adhesion with a semiconductor substrate, fire-through of an antireflection film, contact resistance with a semiconductor substrate and a diffusion layer of a solar cell. Play a role of reduction.

  The conductive paste is printed directly on the semiconductor substrate by a method such as screen printing or printed on the antireflection film formed on the diffusion layer, and dried at a temperature of about 100 to 150 ° C. for several minutes, and then Baked at about 600 to 850 ° C. for several minutes to form a light incident side electrode or a back side electrode. As the firing conditions, optimum conditions for obtaining good solar cell characteristics differ depending on the conductive paste composition, and therefore conditions suitable for the paste composition are selected.

  The influence of the electrode on the conversion efficiency and the stability of the battery characteristics of the crystalline silicon solar cell is large, and particularly the influence of the light incident side electrode is very large. As a measure of electrode performance, there is a solar cell fill factor (FF). When the series resistance of the solar cell is high, the FF tends to be small, but one of the constituent elements of the series resistance is the contact resistance between the P-type semiconductor and the N-type semiconductor and the electrode. In addition, the series resistance in a solar cell can be evaluated using the slope of the tangent at the Voc point (open voltage point) in the IV (current-voltage) characteristics under light irradiation of the solar cell as an index.

For this reason, for the purpose of obtaining high conversion efficiency and stable characteristics of solar cells, the following methods have been proposed so far in which various additives are blended into the conductive paste for solar cell electrodes.
(I) A conductive paste containing glass frit containing Bi ₂ O ₃ , B ₂ O ₃ , and SiO ₂ (Patent Document 1).
(Ii) A conductive paste in which a metal such as Ti, Zn, or Y or a compound thereof is added as fine particles of 0.001 to 0.1 μm (Patent Document 2).
(Iii) A conductive paste containing Ti, Bi, Co, Zr, Fe, and Cr (Patent Document 3).
(Iv) A conductive paste to which a halide is added (Patent Document 4).

  However, in any of the conductive pastes, a sufficiently high FF (curve factor) cannot be obtained in a solar cell including an electrode formed using the conductive paste, and the FF of the FF due to fluctuations in the firing temperature for forming the electrode is not obtained. There was a problem that the change was large.

Japanese Patent Laid-Open No. 11-329072 JP-A-2005-243500 JP 2001-313400 A JP 2001-118425 A

  The present invention solves the above-mentioned problems, and in particular, an electrode for making ohmic contact with an N-type semiconductor of a crystalline silicon solar cell, and a conductive paste for a solar cell electrode capable of stably obtaining a high FF, and the conductive material It aims at providing the manufacturing method of the solar cell using the electrode (especially electrode on an N type semiconductor) of the solar cell formed by baking a conductive paste, the solar cell provided with the said electrode, and the said conductive paste.

  Generally, in a crystalline silicon solar cell, a group V phosphorus (P) or arsenic (As) component is present in an electrode in contact with an N-type semiconductor, and a group III boron (B ) Component is considered to improve ohmic contact. That is, in the former, when the electrode and the N-type semiconductor are joined, components such as phosphorus (P) in the electrode serve to reinforce the donor level formed in the N-type semiconductor, and in the latter, This is because, when a P-type semiconductor is bonded, boron (component) in the electrode is considered to play a role of reinforcing the acceptor level formed in the P-type semiconductor. From this point, selecting the Sn component, which is the same group IV element as silicon, is a strange selection. However, when the present inventors blended a conductive paste for solar cell electrodes as an Sn compound, the electrode formed using such a paste surprisingly has a low contact resistance, resulting in an excellent FF for solar cells. As a result, the present invention has been completed.

  That is, the present invention is a conductive paste for solar cell electrodes, characterized by containing an organic binder, a solvent, conductive particles, glass frit, and a Sn compound. Moreover, this invention relates to the electrode of the solar cell formed by baking said electrically conductive paste. Furthermore, this invention relates to the solar cell provided with said electrode. In addition, this invention relates to the manufacturing method of the solar cell using said electrically conductive paste.

  According to the conductive paste of the present invention, a high FF solar cell can be obtained, and the performance of the solar cell can be improved.

  The conductive paste for solar cell electrodes of the present invention contains an organic binder, a solvent, conductive particles, glass frit, and a Sn compound.

(1) Organic Binder and Solvent The organic binder and the solvent play a role of adjusting the viscosity of the conductive paste and are not particularly limited. It is also possible to use an organic binder dissolved in a solvent.

  Examples of the organic binder include cellulose resins such as ethyl cellulose and nitrocellulose; (meth) acrylic resins such as polymethyl acrylate and polymethyl methacrylate. Organic solvents include alcohols such as terpineol (α-terpineol). And β-terpineol); esters such as hydroxy group-containing esters (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, butyl carbitol acetate, etc.) can be used.

(2) Conductive particles The conductive particles are not particularly limited, and examples thereof include Ag, Cu, and Ni. Ag is preferable because it can be fired in air. The shape and average particle size of the conductive particles are not particularly limited, and those known in the art can be used. Examples of the shape of the conductive particles include a spherical shape and a flake shape. The average particle size of the conductive particles is preferably 0.05 to 10 μm, preferably 0.1 to 5 μm, from the viewpoint of workability. The average particle size means the average of the particle diameter in the case of a spherical shape, the long diameter of the particle flake in the case of flakes, and the length in the case of needles.

(3) Glass frit The glass frit is not particularly limited, and is a Pb glass frit such as PbO—B ₂ O ₃ —SiO ₂ or the like; Pb free glass frit such as Bi ₂ O ₃ —B ₂ O ₃ —SiO. Examples include _2- CeO ₂ —LiO ₂ —NaO ₂ system. The shape and size of the glass frit are not particularly limited, and those known in the art can be used. Examples of the shape of the glass frit include a spherical shape and an indefinite shape. The average particle size of the glass frit is 0.01 to 10 μm, preferably 0.05 to 1 μm, from the viewpoint of workability. The average particle size is as described above, but in the case of an irregular shape, it means the average of the longest diameters.

(4) Sn compound The conductive paste of the present invention contains a Sn compound. The Sn compound may be used alone or in combination of two or more.

Examples of the Sn compound include Sn oxides, hydroxides, and chlorides. These include hydrates. Preferred are SnO ₂ , Sn (OH) ₂ , SnCl ₄ · 5 hydrate, and the like.

  Moreover, in this specification, the organometallic compound of Sn points out the organic compound containing Sn, and the diketone complex and carboxylate of Sn are mentioned. Examples of the diketone complex include an acetylacetone complex, an acetoacetic acid complex, a diethylmalonic acid ester complex, and a cyclopentadiene complex. Examples of the carboxylate include (meth) acrylate, naphthenate, octylate, stearate, palmitate, etc., preferably Sn acetylacetone complex or tin octylate.

  The Sn compound is usually solid or liquid, and can be blended into the conductive paste as it is. In the case of a solid, although the influence of the shape and size is small, the average particle size is preferably 0.05 to 10 μm from the viewpoint of workability and the like, for example, 0.15 to 5 μm can be used, Further, toluene, ethanol, acetylacetone, methylene chloride or the like can be used as a solvent by being dissolved or dispersed in them.

(5) ZnO and / or TiO ₂
Use of ZnO and / or TiO ₂ in the conductive paste of the present invention is effective in obtaining a high FF. The shape and average particle size are not particularly limited. Examples of the shape include a spherical shape and an indefinite shape. The average particle size is preferably 0.05 to 1 μm from the viewpoint of dispersibility.

  These prevent excessive sintering of the conductive particles during the firing process of the conductive paste, and at the same time, suppress the spread of the liquefied glass derived from the glass frit and create a field where the conductive particles come into contact with the semiconductor surface. It can be considered that it is also useful for obtaining good contact because it can be reduced to a semiconductor by reducing in a reducing atmosphere such as CO derived from an organic binder.

  You may mix | blend arbitrary components, such as a dispersing agent and a plasticizer, with the electrically conductive paste of this invention in the range which does not impair the effect of this invention.

  In the conductive paste of the present invention, the glass frit is 0.5 to 10 parts by weight with respect to 100 parts by weight of the conductive particles from the viewpoint of securing sufficient adhesive strength and suppressing increase in contact resistance. It is preferable that it is 1 to 5 parts by weight. Within this range, good adhesive strength and low contact resistance can be obtained.

  Moreover, it is preferable that a Sn compound is 0.001-15 weight part with respect to 100 weight part of electroconductive particles. If it is within this range, the effect of blending can be easily obtained.

Furthermore, when blending ZnO and / or TiO ₂ , these are preferably 0.5 to 15 parts by weight, more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the conductive particles. If it is within this range, the effect of blending can be easily obtained. When using a ZnO and / or TiO _2, Sn compound, the lower range limit near (e.g., with respect to 100 parts by weight of the conductive particles, 0.001 to 5 parts by weight) can exhibit a high effect even .

  The amount of the organic binder and the solvent can be appropriately selected so as to have an appropriate viscosity according to the method for applying and printing the conductive paste.

One of preferred embodiments is for a solar cell electrode containing an organic binder, a solvent, conductive particles, glass frit, and 0.5 to 15 parts by weight of SnO _{2 with} respect to 100 parts by weight of the conductive particles. It is a conductive paste.

Another preferred embodiment is an organic binder, a solvent, conductive particles, glass frit, 0.5 to 15 parts by weight of ZnO and / or TiO _{2 with} respect to 100 parts by weight of the conductive particles, Sn compound 0. It is a conductive pace for solar cell electrodes containing 001-5 weight part.

The method for producing the conductive paste of the present invention is not particularly limited, and an organic binder, solvent, conductive particles, glass frit, Sn compound, and optionally ZnO, TiO ₂ , and other optional components, first a planetary mixer, etc. By kneading and then dispersing with a three roll (made of metal or ceramic) or the like.

  Since the conductive paste of the present invention can be used for manufacturing an electrode for a solar cell and can obtain good contact with an N-type semiconductor, the electrode on the N-type semiconductor (for example, an N-type diffusion layer). Is useful for forming.

  The production of the solar cell electrode and the production method of the solar cell are not particularly limited. An example will be described with reference to FIG.

  A texture is optionally formed on the surface of the P-type polycrystalline silicon substrate 4, and then P (phosphorus) or the like is thermally diffused at 900 ° C. to form the N-type diffusion layer 3. Next, an antireflection film 2 such as a silicon nitride thin film or titanium oxide is formed to a thickness of 50 to 100 nm by a plasma CVD method or the like. As the light incident side electrode, the conductive paste of the present invention is screen-printed on the antireflection film 2, and the solvent is evaporated at about 150 ° C. and dried. Next, as the back surface side electrode, an aluminum electrode paste is optionally printed on the back surface of the P-type polycrystalline silicon substrate 4 by screen printing and dried. Next, baking is performed to obtain a solar battery cell including the light incident side electrode 1 and the back surface electrode 5.

  The solar cell in the examples was manufactured as follows. A texture was formed by wet etching on the surface of a P-type polycrystalline silicon substrate (substrate thickness 200 μm) doped with B (boron). Thereafter, P (phosphorus) was thermally diffused to form an N-type diffusion layer (thickness 0.3 μm). Next, an antireflection film comprising a silicon nitride thin film (thickness: about 60 nm) was formed from silane gas and ammonia gas by plasma CVD. The obtained substrate with antireflection film was cut into 15 mm × 15 mm for use.

  A paste prepared by mixing the components shown in the table below (parts by weight) with a planetary mixer and three rolls is screen-printed on the antireflection film so that the film thickness is about 20 μm. It printed with the pattern which consists of an electrode and a finger electrode, and dried at 150 degreeC for about 1 minute.

  Next, the aluminum electrode paste was printed on the back surface of the P-type polycrystalline silicon substrate 1 by screen printing so that the film thickness was about 20 μm, and dried at 150 ° C. for about 1 minute.

  Thereafter, the substrate on which the paste on both sides was printed and dried was baked at a peak temperature of 725 ° C. for 2 minutes in-out to obtain a solar battery cell provided with a light incident side electrode and a back electrode.

The current-voltage characteristics of the solar battery cells were measured under solar simulator light (AM1.5, energy density 100 mW / cm ² ), and FF was calculated from the measurement results.

  The composition of each conductive paste is as shown in Table 1 below. The FF value is also shown. The examples all showed better FF than the comparative examples containing no Sn compound.

This is the basic structure of a solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light incident side electrode 2 Antireflection film 3 N type diffused layer 4 P type silicon substrate 5 Back surface electrode

Claims (10)

  A conductive paste for solar cell electrodes, comprising an organic binder, a solvent, conductive particles, glass frit, and a Sn compound.   The conductive paste according to claim 1 for forming an electrode on an N-type semiconductor.   The electrically conductive paste of Claim 1 or 2 whose Sn compound is 0.001-15 weight part with respect to 100 weight part of electroconductive particles.   The electrically conductive paste of any one of Claims 1-3 whose Sn compound is an oxide, hydroxide, chloride, or organometallic compound of Sn. Furthermore, ZnO and / or containing TiO _2, any one of claims conductive paste of claims 1 to 4. The conductive paste according to claim 1, comprising an organic binder, a solvent, conductive particles, glass frit, and 0.5 to 15 parts by weight of SnO _{2 with} respect to 100 parts by weight of the conductive particles. 0.5 to 15 parts by weight of ZnO and / or TiO ₂ and 0.001 to 5 parts by weight of Sn compound with respect to 100 parts by weight of the organic binder, solvent, conductive particles, glass frit, and conductive particles The electrically conductive paste of Claim 1 containing these.   The electrode on the N type semiconductor of the solar cell formed by baking the electrically conductive paste of any one of Claims 1-7.   A solar cell comprising the electrode according to claim 8 on an N-type semiconductor.   The manufacturing method of the solar cell which forms the electrode by apply | coating the electrically conductive paste of any one of Claims 1-7 on an N-type semiconductor, making it dry depending on the case, and baking.