Film-forming material

Abstract

There is provided a novel material used for solar cells that can contribute to the improvement in maximum output of solar cells. A film-forming material for forming a light-collecting film on a transparent electrode of a solar cell, including an aromatic group-containing organic polymer compound (A), wherein the film-forming material exhibits an index of refraction of 1.5 to 2.0 at a wavelength of 633 nm and a transmittance of 95% or more with respect to light having a wavelength of 400 nm, and a solar cell obtained by coating a cured film made from the film-forming material on a surface of a transparent electrode.

Claims

1. A film-forming material for forming a light-collecting film on a transparent electrode of a solar cell, the film-forming material comprising: (I) an aromatic group-containing organic polymer compound (A) that is a compound having a fluorene skeleton, having an aromatic cardo structure and a structure of the formula (1), and having a weight average molecular weight of at least 5,000, aromatic cardo structures being linked through a structure containing an ether bond and a thioether bond: ##STR00009## where R.sup.1 to R.sup.10 are independently a hydrogen atom, a C.sub.1-10 alkyl group, a C.sub.1-10 haloalkyl group, a C.sub.1-10 alkoxy group, a halogen atom, a nitro group, a formyl group, a cyano group, an amino group, a carboxyl group, a phosphonyl group, a sulfonyl group, a phenyl group which is optionally substituted with W.sup.8, a naphthyl group which is optionally substituted with W.sup.8, a thienyl group which is optionally substituted with W.sup.8 or a furyl group which is optionally substituted with W.sup.8, provided that one group of R.sup.1 to R.sup.5 forms the —S— group together with one group of R.sup.6 to R.sup.10; and W.sup.8 is a C.sub.1-10 alkyl group, a C.sub.1-10 haloalkyl group, a C.sub.1-10 alkoxy group, a hydroxy group, a halogen atom, a nitro group, a formyl group, a cyano group, a carboxyl group, a phosphonyl group or a sulfonyl group, wherein the aromatic group-containing organic polymer (A) is a compound obtained by carrying out condensation reaction of at least one compound having an aromatic cardo structure and at least one compound having the structure of the above formula (1), wherein the compound having a structure of the formula (1) is selected from the group consisting of: bis(4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-butyl-6-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-isobutyl-6-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-t-butyl-6-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-butyl-5-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-isobutyl-5-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-t-butyl-5-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-methyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-ethyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-propyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-isopropyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-butyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-isobutyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-t-butyl-4-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-butyl-6-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-isobutyl-6-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-t-butyl-6-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-butyl-5-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-isobutyl-5-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-t-butyl-5-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-methyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, bis(2-ethyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-propyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-isopropyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-butyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-isobutyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, (2-t-butyl-3-(oxiran)-2-ylmethoxy)phenyl)sulfane, and bis(4-(oxirane-2-ylmethoxy)-2,3-diamyl-phenyl)sulfane; and (II) as a component (C) a compound substituted with a blocked isocyanate group; wherein the film-forming material exhibits an index of refraction of 1.5 to 2.0 at a wavelength of 633 nm and a transmittance of 95% or more with respect to light having a wavelength of 400 nm.

2. The film-forming material according to claim 1, wherein the organic polymer compound (A) is a compound having at least four benzene rings.

3. The film-forming material according to claim 1, wherein the film-forming material contains the component (C) at 10 to 100 parts by mass relative to 100 parts by mass of the organic polymer compound (A).

4. The film-forming material according to claim 1, wherein the film-forming material further contains a solvent (E) and is in a form of varnish.

5. A solar cell obtained by coating a cured film made from the film-forming material according to claim 1 on a surface of a transparent electrode.

Description

EXAMPLES

(1) The present invention is further described in detail hereinafter by referring to Examples which do not limit the present invention.

(2) Abbreviations and compounds used in the following Examples are as follows.

(3) <Monomers, Cross-Linkers>

(4) NIKALAC MW-390: a melamine compound (hexamethoxymethylated melamine compound) from Sanwa Chemical Co., Ltd.;

(5) CYMEL 1123: a melamine compound (methoxymethylated benzoguanamine compound) from Nihon Cytec Industries Inc.;

(6) NIKALAC MX-270: a urea compound from Sanwa Chemical Co., Ltd.;

(7) ##STR00008##

(8) VESTAGON (Registered trademark) B 1065: a blocked isocyanato compound from Evonik Degussa Japan.

(9) <Adherence Agent>

(10) LS-2450: 3-aminopropyldiethoxymethylsilane from Shin-Etsu Chemical Co., Ltd.

(11) <Solvents>

(12) PGMEA: propylene glycol monomethyl ether acetate;

(13) PGME: propylene glycol monomethyl ether;

(14) HBM: methyl 2-hydroxyisobutyrate;

(15) NMP: N-methyl-2-pyrrolidone;

(16) CHN: cyclohexanone;

(17) EL: ethyl lactate; and

(18) γ-BL: γ-butyrolactone.

(19) <Surfactant>

(20) MEGAFAC R-30: from DIC Corporation.

(21) <Solar Cell Unit>

(22) A 125-mm rectangular crystalline silicon cell unit from Motech Industries, Inc.

(23) <Sealing Material>

(24) A sealing material from Sanvic Inc.

(25) <Tab>

(26) A 1.5-mm PV-ribbon wire from Marusho Co., Ltd.

(27) <Back Sheet>

(28) A back sheet from MA Packaging Co., Ltd.

(29) <Strengthened Glass>

(30) A strengthened glass from Shinkyowa Co., Ltd.

(31) [Measurement of Number Average Molecular Weight and Weight Average Molecular Weight]

(32) Polymers obtained according to the following synthesis examples were measured for the weight average molecular weight (hereinafter abbreviated as Mw) and molecular weight distribution using a GPC instrument from JASCO Corporation (with Shodex (Registered trademark) columns KF803L and KF805L) by flowing dimethylformamide as an elution solvent in the columns (column temperature: 50° C.) at a flow rate of 1 ml/min to elute the polymers. Mw is expressed in terms of polystyrene.

(33) [Sample Application]

(34) Film-forming materials were applied on transparent electrodes of the cell units using a spray applicator from YD Mechatro Solutions Inc.

(35) [Measurement of Index of Refraction]

(36) The index of refraction was measured with a high speed spectroscopic ellipsometer M-2000 from J. A. Woollam JAPAN Co., Inc.

(37) [Preparation of Module]

(38) A module was prepared using a laminator LM-50×50-S from NPC Incorporated. On the strengthened glass, the sealing material, the cell unit, the sealing material and the back sheet were mounted in this order and laminated at 130° C. for 20 minutes.

(39) [IV Measurement]

(40) For IV measurement, a solar simulator YSS-150 from Yamashita Denso Corporation was used. The module was irradiated with light for 6 times at 25° C. and the measured IV Batas were averaged.

SYNTHESIS EXAMPLES

Synthesis of Polymer A1 (Synthesis of Polymer Compound Having a Triazine Skeleton)

(41) To a three-neck flask equipped with a condenser after nitrogen substitution, 10.4 g (0.027 moles) of NIKALAC MW-390 and 9.64 g (0.027 moles) of CYMEL 1123 were added in 80 ml of dissolved PGMEA under nitrogen flow, followed by addition of 0.05 g (0.0003 moles) of p-toluenesulfonic acid. The mixture was stirred under heating at 150° C. and the reaction was terminated after 24 hours. The resulting polymer had a molecular weight of 12,000. The resulting solution was heated at 200° C. and the residue was used for calculation of solid matters, which gave a result of 19.56 wt %.

Synthesis of Polymer A2 (Synthesis of Polymer Compound Having a Fluorene Skeleton)

(42) To a three-neck flask equipped with a condenser after nitrogen substitution, 10.3 g (0.029 moles) of 9,9-bis(4-hydroxyphenyl)fluorene and 9.68 g (0.029 moles) of bis(4-(oxiran-2-ylmethyl)phenyl)sulfane were added in 80 ml of dissolved PGME under nitrogen flow, followed by addition of 0.05 g (0.0003 moles) of benzyltrimethylammonium chloride. The mixture was stirred under heating at 120° C. and the reaction was terminated after 24 hours. The resulting polymer had a weight average molecular weight Mw of 6,000. It was heated at 200° C. and the residue was used for calculation of solid matters, which gave a result of 19.99 wt %.

Preparation of Film-Forming Materials: Examples 1 to 4

(43) According to the compositions shown in the following Table 2, the component (A): polymer solution, the component (B) or (C): cross-linker, the component (D): adherence agent, the component (E): solvent and a surfactant were mixed according to Table 1 and stirred at a room temperature (approximately 25° C.) for over 3 hours to obtain a homogeneous solution so that a film-forming material in the form of varnish was obtained.

(44) TABLE-US-00001 TABLE 1 Composition of film-forming materials Component Component Component Component (A) (B) (C) (D) Solvent (E) Surfactant (g) (g) (g) (g) (g) (g) Example 1 A1 — — — PGMEA/EL R-30 100.0 88.2/7.4 0.0002 Example 2 A1 MW-390 — LS-2450 PGME/EL R-30 100.0 2.934 0.002  101/20.5 0.0002 Example 3 A1 MX-270 — — EL/γ-BL R-30 100.0 5.868  114/33.8 0.0002 Example 4 A2 — VESTAGON — CHN R-30 100.0 3.00 126 0.0002

Examples 5 to 10 and Comparative Example: Preparation of Modules and IV Property Evaluation

(45) The obtained film-forming materials in the form of varnish of Examples 1 to 4 were applied on cell units using the spray device and cured prior to the formation of modules. As Comparative Example, a module was prepared in the similar manner except that the film-forming material was not applied. The film-forming materials used, the curing conditions and measured film thickness and index of refraction are shown in Table 2.

(46) The film thickness was measured on a sample obtained after application and curing under the same conditions as described above for the cell units on a Si substrate using a contact-type film thickness analyzer (Dektak 3).

(47) The index of refraction was measured at 633 nm on a sample obtained after application and curing under the same conditions as described above for the cell units on a Si substrate.

(48) The current-voltage (I-V) measurement was conducted using the prepared cell units of Examples and Comparative Example. For each of the obtained short-circuit current (A): Isc, open voltage (V): Voc and maximum power output (W): Pmax, when the measured value for the cell unit of Comparative Example (without film-forming material) was considered as 100%, the relative values (%) of Isc, Voc and Pmax for the cell units of each Example were determined (see the following equations). The obtained results are shown in Table 2.
Isc (%)=100×Example X (Isc value)/Comparative Example (Isc value)
Voc (%)=100×Example X (Voc value)/Comparative Example (Voc value)
Pmax (%)=100×Example X (Pmax value)/Comparative Example (Pmax value)

(49) TABLE-US-00002 TABLE 2 Results of element property evaluation Film- Curing Film Index forming con- thickness of re- Isc Voc Pmax material ditions (μm) fraction (%) (%) (%) Example 5 Example 1 180° C./ 1.0 1.64 100 100 101 10 min. Example 6 Example 2 180° C./ 0.5 1.62 100 100 103 10 min. Example 7 Example 2 180° C./ 1.0 1.63 100 100 102 30 min. Example 8 Example 2 230° C./ 1.0 1.64 100 100 101 30 min. Example 9 Example 3 180° C./ 1.0 1.64 100 100 101 10 min. Example 10 Example 4 180° C./ 1.0 1.64 100 100 102 10 min. Comparative — — — — 100 100 100 Example

(50) [Evaluation Results]

(51) As shown in Table 2, it is apparent from the results of Examples 5 to 10 that the film-forming materials of the present invention allow increase in the maximum power output (Pmax) by 1 to 3%.