JP2016092354A - Seal film for solar battery and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seal film for a solar battery which can suppress occurrence of a PID phenomenon even with a solar battery module used in a photovoltaic power generation facility with a high system voltage, and a solar battery module which never causes a PID phenomenon.SOLUTION: A seal film for a solar battery comprises an ethylene-vinyl acetate copolymer as a primary resin material and in addition, an organic peroxide as a crosslinking agent and a crosslinking assistant agent. The seal film further comprises at least one kind of carboxylic acid having a valence of 2 or greater. The carboxylic acid having a valence of 2 or greater is trimesic acid.SELECTED DRAWING: None

Description

  The present invention relates to an encapsulating film for solar cells mainly composed of an ethylene-vinyl acetate copolymer and a solar cell module using the encapsulating film, and in particular, PID (Potential Induced) that occurs as a problem of reduced output in the solar cell module. It is related with the sealing film for solar cells which can suppress a Degradation phenomenon.

  In recent years, solar cells that convert sunlight light energy into electrical energy have become widespread as clean energy, and there are many efforts as a power generation business for industrial use, as well as large-scale solar power generation facilities with an output of 1 MW or more. is increasing.

  In addition, a high system voltage is required for reasons such as improving the efficiency of the power transmission system, and solar power generation facilities having a system voltage of 1000 V or higher have been constructed.

  In such a high system voltage solar power generation facility, there is a problem that degradation that causes a decrease in the output of the solar cell module, which is called a PID phenomenon, has not occurred in the conventional solar cell module. This PID phenomenon is caused by the occurrence of a leakage current due to a potential difference between the cell and the frame due to the high voltage of the system.

  This is a phenomenon in which polarization of charges occurs in the internal circuit of the solar cell module, and the output is significantly reduced by preventing the movement of electrons inside the cell. The PID phenomenon is the phenomenon of each member of the solar cell module. This phenomenon is caused by the influence, and studies for suppressing the occurrence of each member are underway.

  As a sealing film used for a solar cell module, a highly transparent resin mainly containing an ethylene vinyl acetate copolymer (hereinafter also referred to as EVA) and various ethylene-α olefin copolymers is used. Yes.

  The sealing material of the solar cell is preferably as transparent as possible, does not absorb or reflect incident sunlight, and transmits most of sunlight, and EVA has a high VA content. Resin is used.

  However, EVA resin having a high VA content is likely to allow electricity to flow, resulting in a decrease in insulation. Moreover, since the transparency of EVA depends on the VA concentration, if other resins or fillers are added to highly transparent EVA in order to improve insulation, the transparency is lowered.

  The role of the sealing film is important in order to maintain the insulation between the cell and the frame, and it is considered that the PID phenomenon can be suppressed by providing the effect of preventing leakage current.

  As a sealing film for solar cells, in order to improve film strength, heat resistance, durability, weather resistance, adhesion, and the like, a crosslinking agent for initiating a crosslinking reaction and a crosslinking assistant for improving the crosslinking density as necessary. A silane coupling agent that improves the adhesive and adhesiveness is blended.

  With only the additive as described above, sufficient insulation as a sealing film having PID resistance cannot be obtained even with a formulation considering insulation.

The insulating property of the sealing film is substituted with a volume resistivity. The volume resistivity having an effect of suppressing the PID phenomenon is 1 × 10 ¹⁵ Ω · cm or more, and there are various methods for improving the volume resistivity.

  As the simplest method, the volume resistivity is improved by a method of containing an insulator such as an inorganic filler in the sealing film or by mixing a resin having a high volume resistivity. Patent Document 1 describes a solar cell encapsulant in which volume resistivity is improved by adding metakaolin.

  When measuring the volume resistivity, it is measured with a constant area x thickness, so the inorganic filler and resin mixing are effective as insulation, but in order to suppress the PID phenomenon, the leakage current flowing from the cell to the frame Therefore, it is necessary to improve the volume resistivity of the entire sealing film.

  In addition, containing an inorganic filler or a resin having a high volume resistivity causes a filler or resin having low transparency to be mixed into a highly transparent resin selected as a sealing film, and as a sealing film There is a risk of lowering the transmittance, which is a fatal deterioration of the sealing film used in a solar cell module that converts sunlight into electric energy.

  Furthermore, containing an inorganic filler or a resin having a high volume resistivity may reduce the adhesion of a sealing film that needs to be adhered to glass or a back sheet. Adhesion with glass and backsheet is an important characteristic in terms of preventing moisture from entering in long-term reliability.

Japanese Unexamined Patent Publication No. 2013-64115

  An object of the present invention is to provide a solar cell sealing film capable of suppressing the occurrence of the PID phenomenon even in a solar cell module used in a solar power generation facility with a high system voltage. The object is to provide a solar cell module free from generation.

As means for solving the above problems, the invention according to claim 1 is for a solar cell in which an ethylene-vinyl acetate copolymer is used as a main resin material and an organic peroxide and a crosslinking aid are added as a crosslinking agent. A sealing film,
A sealing film for solar cells, comprising at least one kind of divalent or higher carboxylic acid.

  The invention according to claim 2 is the solar cell sealing film according to claim 1, wherein the divalent or higher carboxylic acid is trimesic acid or adipic acid.

  In addition, the invention according to claim 3 is characterized in that the addition amount of the divalent or higher carboxylic acid is 1.0% by mass or less. It is a stop film.

The invention described in claim 4 is characterized in that the solar cell sealing film has a volume resistivity value of 1 × 10 ¹⁵ Ω · cm or more after the crosslinking reaction. It is a sealing film for solar cells as described in any one of these.

  Moreover, invention of Claim 5 is the solar cell module characterized by using the sealing film for solar cells as described in any one of Claims 1-4.

  By this invention, the volume specific resistance of the whole sealing film can be improved, and the sealing film effective with respect to a PID phenomenon can be provided, without changing the physical property value required until now.

It is the cross-sectional conceptual diagram which showed the structure of the solar cell module which sealed the solar cell with the sealing film for solar cells of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 shows a configuration of a solar cell module in which a solar cell is sealed using a solar cell sealing film of the present invention, and a glass substrate 1 and a back surface side protective member as a surface side transparent protective member on the light receiving surface side. Between the (back sheet) 2, the solar cell sealing film 3 of the present invention, the solar cell 4 made of a power generation element such as silicon, and the solar cell sealing film 3 of the present invention are sandwiched.

  Utilizing the heat applied at the time of solar cell module production, a thermal reaction is caused inside the sealing film to improve the volume resistivity of the entire sealing film, thereby changing the physical property values conventionally required as a sealing film. Therefore, an effective sealing film against the PID phenomenon can be provided.

  In the present invention, the carboxylic acid undergoes esterification reaction and dehydration reaction with alcohol or acid generated by heat treatment, and improves the volume resistivity of the entire sealing film. This is because it has been found that it works effectively against the PID phenomenon without being changed.

  The sealing film for solar cells of the present invention is a sealing film for solar cells in which an ethylene-vinyl acetate copolymer is used as a main resin material and an organic peroxide and a crosslinking aid are added as a crosslinking agent. It contains at least one of the above carboxylic acids.

  Examples of the crosslinking agent that can be used in the present invention include 1,1-di (t-butylperoxy) cyclohexane, 1,1-di (t-hexylperoxy) cyclohexane, 1,1-di (t-hexylperoxy). Cyclohexane, n-butyl 4,4-di- (t-butylperoxy) valerate, t-butylperoxy-3,5,5-trimethylhexanoate, 2,5-dimethyl-2,5-di (t Organic peroxides such as -butylperoxy) hexane, t-butylcumyl peroxide, 2,2-di- (t-butylperoxy) butane, and t-butylperoxy-2-ethylhexyl monocarbonate.

  Examples of the crosslinking aid that can be used in the present invention include triallyl isocyanurate, diallyl phthalate, triallyl cyanurate, and the like.

  Examples of divalent or higher carboxylic acids that can be used in the present invention include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, citric acid, Examples include nitrilotriacetic acid and ethylenediaminetetraacetic acid.

  Hereinafter, description will be made based on examples.

As a sealing film for solar cell modules,
Ethylene vinyl acetate copolymer 100 parts by mass Crosslinking agent: 2,5-dimethyl-2,5-di (t-butylperoxy) hexane 0.8 part by mass Crosslinking aid: triallyl isocyanurate 0.5 part by mass silane Coupling agent: γ-methacryloxypropyltrimethoxysilane 0.3 part by mass Carboxylic acid: trimesic acid (trivalent) 0.3 part by mass was blended and extruded to a thickness of 0.45 mm. A solar cell sealing film was obtained.

  Sealing for solar cell of Example 2 having a thickness of 0.45 mm under the same conditions except that adipic acid (divalent) was used instead of trimesic acid (trivalent) which is the carboxylic acid used in Example 1 A film was obtained.

<Comparative Example 1>
A solar cell sealing film of Comparative Example 1 having a thickness of 0.45 mm was obtained under the same conditions as in Examples 1 and 2 except that the carboxylic acid used in Examples 1 and 2 was not used.

<Comparative Example 2>
A sealing film for solar cell of Comparative Example 2 having a thickness of 0.45 mm was obtained under the same conditions except that stearic acid (monovalent) was used instead of the carboxylic acid used in Examples 1 and 2.

<Volume specific resistance>
The produced four types of solar cell sealing films were cut into 15 cm squares and sandwiched between Teflon (R) sheets. The sample sandwiched between Teflon (R) sheets was sandwiched between tempered glass for solar cells and a back sheet, and heat treatment was performed using a vacuum laminator.

The conditions of the vacuum laminator are set at 145 ° C., the vacuum process is 4 minutes, the pressurization process is 2 minutes, and the holding process time required for crosslinking is 0 minutes, 2 minutes, 4 minutes, 6 minutes, 8 minutes, 10 minutes, An evaluation sample was prepared under 6 conditions, and the volume resistivity was measured based on the standard number ASTM D257. As an evaluation standard, a sample showing a value of 1 × 10 ¹⁵ Ω · cm or more was regarded as a good product.

<Total light transmittance>
The total light transmittance is the transparency necessary for the sealing film, and was measured based on JIS standard JIS K7105. As an evaluation standard, a non-defective product having an initial value of 90% or more was determined.

<Glass adhesion>
The glass adhesion of the sealing film is indispensable for the stability of the solar cell module, and the value was obtained at a speed of 300 mm / min using a tensile tester and a 180 degree peel test. The adhesion between the test sample and glass was measured. As an evaluation standard, 100 N / cm or more was regarded as a good product.

<PID evaluation>
For the PID test, a four-crystal module of a single crystal Si cell was prepared and used for evaluation. In the PID test, the IV characteristics (Pm, Voc, Isc, FF) in the initial state of the sample module are measured, the sample is placed in a constant temperature and humidity chamber set to 60 ° C./85% RH, and water is placed on the glass surface. The positive output terminal and the negative output terminal were applied to the negative electrode, and the metal frame was applied to the positive electrode at a voltage of 1000 Vdc.

  The sample module was taken out after 96 hours, and IV characteristics (Pm, Voc, Isc, FF) after the PID test were measured.

As an evaluation standard for PID evaluation, the Pm retention rate of the value after the PID test with respect to the initial value of the IV characteristic is judged,
Pm (W): 90% or more.

  Table 1 shows the evaluation results of volume resistivity, total light transmittance, glass adhesion, and PID test for the solar cell sealing films of Examples 1 and 2 and Comparative Examples 1 and 2.

The solar cell sealing film of Example 1 to which trimesic acid (trivalent), which is a divalent or higher carboxylic acid, was added and the solar cell sealing film of Example 2 to which adipic acid (divalent) was added were An increase in the specific resistance was confirmed, and the volume specific resistance value measured based on ASTM D257 was 1 × 10 ¹⁵ Ω · cm or more.

Among them, the effect of trimesic acid (trivalent), which is a tricarboxylic acid, was large and was an effective material in the present invention. On the other hand, the solar cell sealing film of Comparative Example 1 in which no carboxylic acid was added and Comparative Example 2 in which the monovalent carboxylic acid stearic acid was added had no increase in volume resistivity, and the volume resistivity value was 1 ×. The evaluation criteria of 10 ¹⁵ Ω · cm or more could not be satisfied.

  The solar cell encapsulating film of Example 1 to which trimesic acid was added and the solar cell encapsulating film of Example 2 to which adipic acid was added resulted in significantly improved Pm retention and the suppression of the occurrence of the PID phenomenon. It became. On the other hand, in Comparative Example 1 containing no carboxylic acid, a decrease in output occurred after the PID test.

  In the case of containing an inorganic filler or a resin having a high volume resistivity, a decrease in transmittance and a decrease in adhesion force occur, but in the present invention, no decrease is observed in the initial values of the total light transmittance and the glass adhesion force. The effect of the present invention became clear.

DESCRIPTION OF SYMBOLS 1 ... Glass substrate as a surface side transparent protective member at the light-receiving surface side 2 ... Back side protective member (back sheet)
3 ... Solar cell sealing film 4 ... Solar cell

Claims (5)

It is an encapsulating film for solar cells in which an ethylene-vinyl acetate copolymer is used as a main resin material, an organic peroxide is added as a crosslinking agent, and a crosslinking aid is added.
A sealing film for solar cells, comprising at least one kind of divalent or higher carboxylic acid.   The solar cell sealing film according to claim 1, wherein the divalent or higher carboxylic acid is trimesic acid or adipic acid.   The solar cell sealing film according to claim 1 or 2, wherein an addition amount of the divalent or higher carboxylic acid is 1.0 mass% or less. The volume specific resistance value after the crosslinking reaction of the sealing film for a solar cell is 1 × 10 ¹⁵ Ω · cm or more, for a solar cell according to any one of claims 1 to 3. Sealing film.   The solar cell module using the sealing film for solar cells as described in any one of Claims 1-4.