KR101009319B1 - Polynorbornenedicarboximide film modified with trifluoromethoxyphenyl and Organic light-emitting device using the same - Google Patents

Abstract

Indium tin oxide (ITO) deposited on a polynorbornenedicarboxyimide substrate in which the N position of the imide is substituted with trifluoromethoxyphenyl, and a hole transport layer and electrons sequentially deposited on the indium tin oxide (ITO) An organic electroluminescent device comprising a transport layer and a cathode is disclosed.

TFMONDI, polynorbornene dicarboxyimide, heat resistance, transmittance, refractive index

Description

Polynorbornenedicarboxyimide film containing trifluoromethoxyphenyl and organic electroluminescent device using the same {Polynorbornenedicarboximide film modified with trifluoromethoxyphenyl and Organic light-emitting device using the same}

The present invention relates to a polynorbornene dicarboxyimide film comprising trifluoromethoxyphenyl which is transparent, high heat resistance, and has a low refractive index and dielectric constant, and an organic electroluminescent device using the same.

Recently, a lot of research is being conducted on flexible displays that can be functioned without bending, bending, or rolling without loss of display performance. Substrates of such flexible displays require high heat resistance, transparency, and low moisture permeability.

Polymeric materials have the disadvantage of being weak to heat, but they are gaining attention as flexible display materials in the future because they are transparent, flexible, light, and cheaper than other materials. As polymer flexible substrate material, polyethylene naphthalate (PEN) film with improved heat resistance, polycarbonate (PC) film with excellent transparency and heat resistance, and polyether sulfone (PES) with better heat resistance than polycarbonate are used as flexible substrate. Many studies have been conducted for this purpose, and the use of polyimide (PI), cyclic olefin copolymer (COC), and polyarylate (PAR) is also being considered.

However, the above polymers do not satisfy all of high heat resistance, high transparency, and low moisture permeability.

On the other hand, Korean Patent Publication No. 1989-0000559 discloses the synthesis of polynorbornene dicarboxyimide in which the N-position of the imide is substituted with phenyl. However, the material has only been studied for its potential as an excellent gas-selective film, and has not yet been mentioned for its optical properties and its application as a substrate for flexible organic electroluminescent devices.

In order to increase the efficiency of the flexible organic electroluminescent device, the refractive index of each layer constituting the device should be low. In particular, since the external efficiency almost depends on the refractive index of the substrate, a substrate having a lower refractive index than glass is required to have a high external efficiency.

An object of the present invention is to provide a polynorbornene dicarboxyimide film having a trifluoromethoxyphenyl group having a higher heat resistance, higher transmittance, and a lower refractive index than a conventional transparent polymer film, and an organic electroluminescent device using the same.

The above object is achieved by polynorbornene dicarboxyimide containing trifluoromethoxyphenyl for application as a substrate of an organic electroluminescent device having high heat resistance and low refractive index and dielectric constant.

In addition, the above object is an indium tin oxide (ITO) or zinc oxide formed on a polynorbornene dicarboxyimide substrate in which the N position of the imide is substituted with trifluoromethoxyphenyl, and the indium tin oxide (ITO). Or an organic electroluminescent device comprising a hole transport layer, an electron transport layer, and a cathode sequentially deposited on zinc oxide.

The polynorbornene dicarboxyimide is a first step of converting the nordonene dicarboxylic anhydride which is an endo isomer into an exo isomer; A second step of synthesizing norbornene anhydride dicarboxylic acid of exo isomer with N-trifluoromethoxyphenylnorbornenedicarboxyimide; And a third step of synthesizing N-trifluoromethoxyphenylnorbornenedicarboxyimide into poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide).

The first step is a step of heating the norbornene dicarboxylic anhydride iso isomer is at least 220 ℃ under a nitrogen atmosphere, then slowly cooled to 120 ℃; At 120 ° C., adding chlorobenzene to the polynorbornenedicarboxylic anhydride; After the mixture is cooled to room temperature, the crystals are filtered, washed, and dried to include trifluoromethoxyphenyl groups.

The second step is a step of sufficiently dissolving norbornene anhydride dicarboxylic acid of the exo isomer in toluene; Adding and stirring 4-trifluoromethoxyaniline to the norbornene anhydride dicarboxylic acid solution; Filtering and drying the suspension to form amic acid when the suspension is formed; The amic acid is stirred, refluxed in sodium acetate anhydrous, acetic anhydride solvent, and recrystallized with methanol.

Preferably, the molar ratio of the amic acid, sodium acetate anhydride, and acetic anhydride is 7: 4: 64.

The third step comprises the steps of dissolving N-trifluoromethoxyphenylnorbornenedicarboxyimide in a dichloroethane solvent in a nitrogen atmosphere; Stopping the reaction by adding ethylvinyl ether in a nitrogen atmosphere; Solidifying by adding methanol at room temperature; And dissolving the polymer in chloroform and adding hydrochloric acid.

Preferably, a polymerization initiator may be added at the time of dissolving the N-trifluoromethoxyphenylnorbornenedicarboxyimide.

Here, the polymerization initiator may be a ruthenium catalyst.

As described above, the polymer according to the present invention is very transparent, thermally stable, and has a low refractive index and dielectric constant. When indium tin oxide was deposited on the polymer film, its performance increased with temperature, and as a result, it was found that the electrical and optical properties were excellent by having a high gain index.

In addition, when the organic light emitting device was manufactured using the polymer as a substrate, there was almost no difference in performance compared to when the device was manufactured using glass as the substrate. Could. This proved that the polymer can be sufficiently used as a substrate of a flexible organic light emitting device, and is expected to be useful in the optical device industry requiring high thermal stability and transparency as well as wave guides.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The inventors of the present invention, using polynorbornene dicarboxyimide to substitute trifluoromethoxyphenyl at the N-position of the imide to produce a polymer film having high heat resistance, high transparency and low refractive index, using the substrate as a substrate As a result, indium oxide (ITO), which is an anode material, was formed and an organic electroluminescent device was manufactured using the same. As the indium tin oxide (ITO) target for sputtering, those made of 90 wt% indium oxide (In ₂ O ₃ ) and 10 wt% tin oxide (SnO ₂ ) were used.

[Example]

<Synthesis of polynorbornene dicarboxyimide containing trifluoromethoxyphenyl group at N position of imide>

Endo isomer chain Of norbornene dicarboxylic anhydride Exo  Conversion to isomers

Endonene dicarboxylic anhydride, an endo isomer, is placed in a two-necked round flask to bring the inside into a nitrogen atmosphere. After heating at 220 ° C. for about 2 hours, the mixture is slowly cooled to 120 ° C. When the temperature reaches 120 ° C., chlorobenzene is added in a 1/2 molar ratio of polynorbornenedicarboxylic anhydride. After cooling to room temperature, the white crystals are filtered off, washed with methanol and dried in a vacuum oven at 60 ° C.

Synthesis of N-trifluoromethoxyphenylnorbornenedicarboxyimide

The norbornene anhydride dicarboxylic acid of the exo isomer is fully dissolved in toluene. At this time, the concentration of the solvent is to be 4 to 5% by weight. 4-trifluoromethoxyaniline, the reactant, is added in 5-10% excess of the same number of moles of norbornene monomer, dropwise dropwise into norbornene anhydride dicarboxylic acid solution, and reacted by stirring at 50 ° C for 3 hours. Once the suspension is made, it is filtered and dried. The obtained amic acid is stirred and refluxed with anhydrous acetic acid solvent for 2 hours with sodium anhydride. At this time, the molar ratio of amic acid, sodium acetate anhydride and acetic anhydride is preferably 7: 4: 64. After cooling to room temperature, the obtained crystals are washed several times with water and recrystallized twice with methanol.

Synthesis of Poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide)

N-trifluoromethoxyphenylnorbornenedicarboxyimide is dissolved completely in dichloroethane solvent. At this time, the concentration of the solvent is 20% by weight. Ruthenium catalyst is used as a polymerization initiator. Ruthenium catalyst is the same as [Formula 1]. The initiator is added at a 1/100 molar ratio of N-trifluoromethoxyphenylnorbornenedicarboxyimide and stirred at 60 ° C for 4 hours. The reaction must be reacted in a nitrogen atmosphere. The polymerization is stopped by adding ethylvinyl ether in a nitrogen atmosphere. After cooling to room temperature, the polymerized solution is poured into excess methanol to solidify, the polymer is dissolved in chloroform, and a few drops of 1 normal hydrochloric acid are added. It was again poured into methanol to solidify and dried in a vacuum oven at 40 ° C. After this process two or three times, a pure polymer can be obtained.

<Production of Poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) Film>

When the polymer is dissolved in 5% by weight of N, N-dimethylacetamide, which is a polar aprotic solvent, a high concentration solution can be obtained. This solution is poured into a clean glass plate and dried sufficiently in an oven to obtain a transparent film. The obtained transparent film is shown in FIG.

<Transparent electrode film formation and organic electroluminescent device fabrication>

The polynorbornene dicarboxyimide in which the N position of the imide was substituted with trifluoromethoxyphenyl was used as a substrate. Indium tin oxide (ITO), a cathode material, is formed by using magnetron sputtering. The film forming conditions were 80 W of R.F. power, 120 nm of indium tin oxide (ITO) thickness, the pressure of argon gas was 1.0 Pa, and the distance between the target and the substrate was 50 mm. Film-forming temperature shall be 25 degreeC, 100 degreeC, 150 degreeC, and 200 degreeC.

Here, zinc oxide (ZnO) may be applied instead of indium tin oxide (ITO).

A flexible organic electroluminescent device was manufactured by thermal evaporation on an indium tin oxide (ITO) film prepared above. The organic material in the interior is most commonly used, and in the hole transport layer, N, N'-diphenyl-N, N '-(3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD ) Was deposited to 50 nm, and tris (8-hydroxyquinolinato) aluminum (Alq 3) serving as a light emitting layer and an electron transporting layer was deposited to a thickness of 70 nm, respectively. Finally, 100 nm of aluminum, a cathode material, was deposited to fabricate an organic electroluminescent device.

<Characteristics of Poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) Film>

Figure 2 shows the result of measuring the thermal stability by TGA (Q50 Q Series) of TA Instrument, Figure 3 shows the result of measuring the coefficient of thermal expansion (Coefficient of Thermal Expansion) through a thermomechanical analyzer (SEIKO TMA 320).

The above thermal characteristics are shown in Table 1.

Tg (占 폚) Td (℃) CTE (50 to 200 ° C) ppm / ° C Poly (TFMONDI) 230 440 109

The glass transition temperature is 230 ℃, the decomposition temperature is 440 ℃, and the thermal expansion coefficient is 50 ~ 200 to 109ppm / ℃, and the thermal stability is good, and it is superior to the previous polynorbornene. This is because a large group such as trifluoromethoxyphenyl is introduced at the N-position of the polynorbornenedicarboxyimide group to reduce the rotation and mobility of the molecular chain.

4, the optical properties of the polymer were confirmed by UV-Vis spectra (U-2010, HITACHI). The polymer shows a transmittance of 90% or more in the visible light region 400 ~ 700nm. Therefore, the polymer may be considered to be very transparent.

Table 2 shows the results of the refractive index and the dielectric constant measured by the Prism coupler.

Optical properties at 632.8 nm (474.08 THz) n _xy n _z Δ n _b ε _xy ε _z ε _b Poly (PhNDI) 1.531 1.537 0.007 1.533 2.343 2.363 2.350

The laser (He-Ne) source used a 632.8 nm wavelength and operates at 1 Hz. The in-plane and out-of-plane values were calculated by the measured values n _xy and n _z , and Δ was the birefringence value calculated by the formula of n _xy -n _z . n _b is the mean of n _xy and n _z . ε _xy And _εZ is Maxwell's equation for the in-plane and out-of-plane of the Maxwell's equation (ε = n ² Calculated by ε _b is the average of ε _xy and ε _z .

The sample was spin coated onto a silicon wafer and the film thickness was 15 ± 1 μm. The refractive index is 1.533, which is lower than that of glass used in basic devices, and the dielectric constant obtained by Maxwell's equation is 2.350, which is lower than that of other polymer transparent films. Therefore, since the refractive index of the substrate that determines the external efficiency of the device is low, it is expected that the external efficiency will be higher than when the device is made of glass. This low index of refraction is due to the fact that the molecular structure of the molecule is mostly ring-shaped, and the electron density of the molecule is lowered because it contains fluorine groups.

In the present invention, crystals of poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) developed using wide-angle x-ray diffraction (WAXD) were identified through FIG. 5. The CuKa radiation (wavelength = 1.54 GHz) source of the igku diffractometer (Model Rigaku Minflex) operates at 50kv and 40mA. Scan data of 2θ were collected at intervals of 0.01 ° and scan speed of 1.0 ° (2θ) / min in the range of 1.2 ° to 40 °.

The polymer is semicrystalline, and the distance between the chains (d value) can be obtained by Bragg (nλ = 2dsinθ) through a crystal peak near 20 °. The distance between the chains is 4.8 Å. According to the literature, when the N-position of the imide is replaced with a group having a size of 4.9 kV when substituted with a cyclopentyl and 5.0 kPa when substituted with a cyclohexyl, the inter-chain spacing increases. As the spacing between the chains increases, the molecular density between the chains increases, which lowers the dielectric constant.

6 is a result of measuring the surface of the polymer by atomic force microscope (Atomic Force Microscope, Nanoscope IIIa). The semi-crystalline polymer was found to have a very low mean square roughness (RMS) value of 0.5 nm. When the polymer is used as a substrate, the smoothness of the surface can be a very important factor in the formation of indium tin oxide (ITO).

<Characteristics of Indium Tin Oxide (ITO) Formed on Poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) Film>

The optical properties of polymer films in which Indium Tin Oxide (ITO) was deposited were investigated using UV-visible spectrometer (U-2010, HITACHI). According to FIG. 7, the transmittance in the visible light region of the polymer film on which the indium tin oxide is formed is shown to be 85% or more. It is 90% or more when ITO is formed at 200 ° C. Referring to FIG. 8, it can be seen that the average transmittance increases as the deposition temperature increases.

Wide angle X-ray diffraction (WAXD) was used to evaluate the structural properties of indium tin oxide (ITO) deposited on the transparent polymer film. The CuKa radiation (wavelength = 1.54 GHz) source of the Rigaku diffractometer (Model Rigaku Minflex) operates at 30kv and 15mA. Scan data of 2θ were collected at intervals of 0.01 ° and scan speed of 1 ° / min over a range of 25 ° to 65 °. 9 shows crystal characteristics at temperatures of 25 ° C., 100 ° C., 150 ° C., and 200 ° C., respectively. Typical orientations (222), (400), (440), and (622) show polycrystals, and the strength of the orientation can be seen to increase with increasing temperature. This means an increase in crystallinity and grain size.

The electrical properties were measured with a sheet resistance meter (CHANGMIN TECH). It was confirmed in FIG. 10 that the electrical sheet resistance improved with increasing temperature. This is because the carrier concentration is increased in the indium tin oxide (ITO) film. That is, the diffusion of tin atoms from the grain boundary into the indium region increased, and the role of the tin atoms as the trivalent indium atoms as the main donors is effective with increasing temperature.

The overall electrical and optical properties of the substrate are explained by the figure of Merit. This is an important indicator of the utility and stability of the transparent electrode. Here, the gain index was calculated by the method described in the literature. (DB Fraser, HD Cook [J. Electochem. Soc., 119, 1368 (1972)] and G. Haacke [J. Appl. Phys., 47, 4086 (1976)]). It can be seen that the value is improved, it has a high average transmittance compared to the general polyimide substrate, and as a result has a high gain index.

Board Film formation temperature (℃) Sheet resistance (Ω / sq.) Average transmittance (%) Gain Index (F _TC ) (× 10 ^-3 Ω ^-1 ) Gain Index (Φ _TC ) (× 10 ^-3 Ω ^-1 )
Poly (TFMONDI)
25 31.8 86.44 27.18 7.32 100 23.3 87.12 37.39 10.81 150 20.6 88.91 43.16 14.98 200 18.8 90.31 48.08 19.20 Polyimide 200 19.8 76.9 38.8 3.6 ITO Glass 150 17.07 91.07 53.35 23.00

<Performance and Stability of Organic Electroluminescent Device>

The organic light emitting device was manufactured by the above-mentioned method on the transparent electrode manufactured at 150 ℃. 11 shows current density and brightness of light with respect to voltage, respectively. In Fig. 12, the EL spectrum of the device fabricated at a film formation temperature of 150 deg. C is shown. The wavelength when the maximum value is shown is 525 nm. This is a typical value when Alq3 is used as a luminescent material, and recombination of electrons and holes occurs mainly in the Alq3 layer.

When the device was bent, it was confirmed that green light appeared clearly, and no electric shock was found. This is the same as the result when the indium tin oxide (ITO) was formed at the same temperature and the same thickness using glass as the substrate and the organic light emitting device was manufactured. Therefore, even if the polymer film of the present invention is used as a substrate of a flexible organic light emitting device it could be confirmed that no effect on the performance and stability of the device.

In the above description, the embodiment of the present invention has been described, but various changes can be made at the level of those skilled in the art. Therefore, the scope of the present invention should not be construed as being limited to the above embodiment, but should be interpreted by the claims described below.

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1 is a photograph showing a flexible and highly transparent poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film.

2 is a graph showing the thermal stability of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film.

3 is a graph showing the coefficient of thermal expansion of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film.

4 is a graph showing the transmittance of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film.

5 is a graph of crystals of poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) measured by wide-angle X-ray diffraction (WAXD).

6 is an image of the surface of poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) measured by atomic force microscope.

7 is a graph showing the transmittance according to the film formation temperature of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film on which indium tin oxide (ITO) was formed.

FIG. 8 is a graph showing average transmittance according to film formation temperature of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film on which indium tin oxide (ITO) was formed.

FIG. 9 is a wide-angle X-ray diffraction (WAXD) graph of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film on which indium tin oxide (ITO) is deposited, according to a film formation temperature.

FIG. 10 is a graph showing sheet resistance according to film formation temperature of a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film on which indium tin oxide (ITO) was formed.

FIG. 11 is a graph showing current density and brightness of light of an organic light emitting device manufactured by using a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film as a substrate.

FIG. 12 is a light emission graph of an organic light emitting device manufactured by using a poly (N-trifluoromethoxyphenylnorbornenedicarboxyimide) film as a substrate.

Claims (5)

A polynorbornene dicarboxyimide film in which the N position of the imide for application to a substrate of an organic electroluminescent device is substituted with trifluoromethoxyphenyl. Indium tin oxide (ITO) deposited on a polynorbornenedicarboxyimide substrate in which the N position of the imide is substituted with trifluoromethoxyphenyl, and a hole transport layer and electrons sequentially deposited on the indium tin oxide (ITO) An organic electroluminescent device comprising a transport layer, and a cathode. A hole transport layer, an electron transport layer, sequentially deposited on zinc oxide (ZnO) and zinc oxide (ZnO) deposited on the polynorbornene dicarboxyimide substrate in which the N position of the imide is substituted with trifluoromethoxyphenyl; And an organic electroluminescent device comprising a cathode. An organic thin film transistor using a polynorbornene dicarboxyimide in which the N position of the imide is substituted with trifluoromethoxyphenyl. An organic solar cell using a polynorbornene dicarboxyimide in which the N position of the imide is substituted with trifluoromethoxyphenyl.

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