KR20170140140A - Self-metered solution-processable organic light-emitting devices based on small molecular emissive layers doped with interface-engineering additives - Google Patents

Abstract

The present invention provides a small molecular organic light-emitting device (SM OLED) which manufactures a light-emitting layer by using a self-measuring solution coating process of an H-dip coating or a slot die coating. The light emitting layer uses 4,4,4-tris(9-carbazolyl)-triphenylamine (TcTa) as a hole transport material, uses 2,7-bis(diphenylphosphoryl)-9,9-spirobifluorene (SPPO13) as an electron transport material, and is doped with blue, green, and red light-emitting fluorescent substances (for example, iridium complex). Moreover, in the present invention, polyoxyethylene(n)tridecyl ether (PTE) is mixed with a low molecular light-emitting layer as an interface-engineering additive for improvement of electron injection and hole blockage characteristics on a cathode interface and improvement of thin film formation.

Description

TECHNICAL FIELD [0001] The present invention relates to a self-metering solution process organic light emitting device based on a low-molecular light emitting layer doped with an interface control additive,

The present invention relates to an organic light emitting device based on a solution process.

Recently, studies on organic semiconductor materials and organic light emitting devices have been increasing, and they have an advantage of being able to realize reasonable cost, light weight, flexing ductility, large area flat panel display and solid light emitting application. In this regard, researchers are seeking to improve efficiency, stability, and device manufacturing processes. In order to improve the efficiency of the OLED, a phosphorescent dopant is fused to emission layers (EMLs) to induce coupling of the spin orbit and rapid crossing of the spin orbit, which leads to efficient emission transition from the triple state to the ground state, The quantum efficiency reached almost 100%. Open No. 10-2015-0070964 also provides an OLED having a concentration gradient of a phosphorescent dopant compound in the light emitting layer. With the use of a phosphorescent material, the OLED has a high luminance of 50,000 to 100,000 cd / m < ² > and a peak efficiency of 25 to 60 cd / A or more. The manufacture of such electroluminescent low molecular weight OLEDs (SM OLEDs) is divided into two categories. That is, solution processes such as vacuum deposition, spin coating, ink jet, and blade coating. Vacuum-deposited SM OLEDs tend to use more complex co-deposition of multiple components to fabricate multi-layered SM OLEDs because they are much better performing than solution process devices. However, in the case of vacuum deposition, expensive organic materials are wasted and manufacturing costs are high. On the other hand, the solution process technique can overcome the disadvantage that co-deposition and accurate doping associated with vacuum are difficult, , Cost efficiency and simplicity of the process. In the proposed solution processes, a mixed host containing a low molecular weight material that transports holes and electrons was used to increase the charge balance and recombination region size of the SM OLED. It has been reported that a peak efficiency of 56.9 cd / A is shown in a solution coated SM OLED including a green phosphor as a doped emissive layer. In the solution process SM OLED, most of the light emitting layers, which consist of precise proportions of multiple components of the mixed host / doped guest, have been produced using the spin coating method. Spin coating technology makes the light emitting layer easily on the substrate. However, due to the limitations of coating area and non-uniform morphology, spin coating is not applicable to high volume production processes. The recent development of solution processes for SM OLEDs has focused on cost-effective methods of SM OLEDs, which have evolved into simplified processes that are more reliable for low molecular weight luminescent layers to form flat and uniform layers across large areas have. Most recently, attempts have been made to prevent the formation of nanopinholes in a solution coated multi-coated light emitting layer using horizontal dip coating (H-dip coating). In OLEDs with solution process, the multi-coated light emitting layer has better performance than the uncoated one. However, compared to other solution processes, multi-coating is more complicated and wastes organic matter, leads to relatively high manufacturing costs, and does not yield high throughput. In addition, the development of alternative simplified coating processes capable of forming a planar, homogeneous light emitting layer and achieving a balance of charge carrier recombination and enabling high efficiency luminescence is essential to obtain a satisfactory SM OLED.

Accordingly, an object of the present invention is to provide a SM OLED which can simplify a manufacturing process, have a low manufacturing cost, can form a flat and uniform light emitting layer, achieve a charge carrier recombination balance of the formed light emitting layer, .

According to the above object, the present invention provides an SM OLED in which a light emitting layer is prepared by using a self-metering solution coating process of H-dip coating, wherein the light emitting layer comprises 4,4 ', 4 " (Diphenylphosphoryl) -9,9'-spirobifluorene (SPPO13) is used as an electron transporting material and doped with blue, green and red luminescent fluorescent material iridium complexes. do.

The present invention also provides polyoxyethylene (n) tridecyl ether (C ₁₃ H ₂₇ (OCH ₂ CH ₂ (CH _{3) 2} ) as an interface-engineering additive for improving electron injection and hole- ) _n OH, n = t to 30, PTE) are mixed in the low molecular weight luminescent layer. At this time, the concentration of the PTE additive introduced into the light emitting layer is 1 wt% or less by weight.

In order to investigate the film forming ability, the coated low molecular weight luminescent layer was examined by atomic force microscopy (AFM) with or without PTE additive. The use of PTE additive significantly reduced defects such as nanopinholes in the light emitting layer, and the surface morphology was uniform and a thin and homogeneous PTE-mixed light emitting layer was formed with only one H-dip coating process.

A simple H-dip coated PTE mixed emissive layer exhibited excellent device performance in SM OLEDs and exhibited excellent performance in blue, green and red SM OLEDs at peak currents of 12.0 cd / A, 31.2 cd / A, and 4.0 cd / 25,600 cd / m ² , 115,000 cd / m ² , and 14,000 cd / m ² , respectively.

Further, the present invention shows the possibility of realizing a SM OLED having a large area applicability and a high performance solution processability by forming a light emitting layer doped with PTE using an H-dip coating.

The present invention also shows that the self-metering process extends also to the slot die coating process, which makes it possible to produce SM OLEDs comparable to those produced using H-dip coatings.

These results clearly show that the H-dip coated PTE mixed low molecular weight luminescent layer can produce a bright SM OLED with a simple and efficient solution process.

They can promise a mass-production alternative for the low molecular weight luminescent layer of vacuum deposition.

Fig. 1 (a) is a layered structure of a SM OLED, and Fig. 1 (b) is a chemical structure of a substance used in EMLs.
2 (a) is PEDOT as a function of the feeding speed U with respect to the two types of gap height h _0:. HILs film thickness of the PSSC graph, Figure 2 (b) is transferred with respect to the two types of gap height h _0. A low molecular blue EML thin film thickness graph with PTE additive as a function of velocity U.
Fig. 3 (a) is a spin-coated one, Fig. 3 (b) is an H-dip coated EML with no PTE additive, and below is an AFM topography of EML with a PTE additive.
Figure 4 (a) shows the current density-voltage ( JV ), Figure 4 (b) luminance-voltage ( LV ), Figure 4 (c) for H- dip coated blue SM OLEDs with and without PTE additive, the voltage (PE-V) characteristic graph - the current efficiency-voltage (LE-V), Fig. 4 (d) is power efficient.
Fig. 5 is a topography of an AFM of a green low-molecular EML. Fig. 5 (a) is spin-coated and Fig. 5 (b) is an H dip coating.
Figure 6 shows (a) JV , (b) LV , (c) LE-V , and (d) PE-V characteristic curves for H dip-coated green SM OLEDs with and without PTE additives.
Fig. 7 is a topography of AFM of a red low molecular weight EML. Fig. 5 (a) is spin-coated and Fig. 5 (b) is H-dip coated.
Figure 8 shows (a) JV , (b) LV , (c) LE-V , and (d) PE-V characteristic curves for H dip coated red SM OLEDs with and without PTE additives.
FIG. 9 (a) is a photograph of blue, green and red SM OLEDs fabricated by a solution process operating at about 10 V showing the EL characteristic efficiency of H dip-coated EML with PTE additive.
10 shows (a) JV (b) LV characteristic curves of self-metering slot die-coated blue SM OLED for EML with and without PTE additive.
11 is a table summarizing performance of co-host (SPPO13: TcTa) guest-based SM OLEDs with or without interfacial control PTE additives.

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

The materials are as follows.

Poly (styrene sulfonic acid) doped poly (3, 4-ethylenedioxythiophene) (PEDOT: PSS, CLEVIOS ( ^TM) PVP AI 4083, HC Starck) was prepared as a hole injecting material. (Lumtec) was used as a hole transporting material, SPPO13 (Lumtec) was used as an electron transporting material, Firpic (Lumtec) was used as a blue luminescent phosphor, and Ir (ppy) was used as a green luminescent phosphor to prepare solution processable light emitting layers (EMLs) ₃ (Lumtec) and Ir (piq) ₂ acac (Lumtec) as a red light emitting phosphor were used without further purification. Interface control additive is _{PTE (C 13 H 27 (OCH} 2 CH 2) n OH, n = 12, Aldrich), Cs 2 CO 3 as an electron injection material (Sigma-Aldrich), and Al (Sigma-Aldrich) added to the negative electrode The product was used as supplied without purification. The chemical structure of the materials used in the EMLs is shown in Figure 1 (b).

The horizontal dip coating (H-dip) is carried out as follows.

The apparatus for H-dip coating is as shown in Fig. 2 (a).

The volume (~ 5 to 10 μl) of the solution per coating area (1 × 1 cm ² ) is small and can be measured using a syringe pump (Pump Systems Inc. NE-1000) to the clearance of a cylindrical H- .

The height of the gap h ₀ is adjusted using a micrometer positioner mounted on the end of the coating head, and the transport speed U is controlled by a computer controlled conversion stage (SGSP26-200, Sigma Koki Co., Ltd). After the meniscus of the coating solution is formed between the H-dip coating head and the substrate, the substrate is transported horizontally, and the H-dip coating head spreads the solution flat onto the substrate while simultaneously applying a downstream meniscus of the solution, Keep the shape. The transporting speed U was set at 1.5 cm / s, and it took about 1 minute to make about 1 m of thin film on the substrate. Thin film production is possible even if the transporting speed U is about 1.0 cm / s to 2 cm / s.

The fabrication of the device is as follows.

As shown in Fig. 1 (a), a solution process SM OLED was fabricated on a glass substrate previously coated with an ITO anode (thickness: 80 nm, sheet resistance: 30 Ω per square). It may be formed on a transparent substrate other than glass. The ITO substrate is ultrasonically cleaned with detergent, deionized water, acetone and isopropanol, blow dried with nitrogen and then subjected to ultra-violet ozone cleaning for 15 minutes. A 40 nm PEDOT: PSS hole-injecting layer (HIL) is H-dip coated on the previously cleaned ITO substrate and then baked at 120 ° C in a vacuum oven for 10 minutes to remove residual moisture.

In order to form the blue SM OLED, 1,2-dichloroethane and chloroform (at a mixing weight ratio of 3: 1) were used as the mixed solvent, and the host and the Firpic fluorescent blue light emitting guest, which were mixed with Ta and SPPO13, A well mixed EL solution was prepared for EMLs by dissolving with additives.

The mixed host was TcTa: SPPO13 at 48% SPPO13 and the concentration of Firpic was maintained at 17% (optimized for blue emission).

Next, the EMLs were H-dip coated onto PEDOT: PSS HIL and then baked in a vacuum oven at 110 ° C for 5 minutes to remove residual moisture and the thickness of the EMLs was about 80 nm. Next, an electron injection interface layer Cs ₂ CO ₃ (2 nm) and an Al cathode layer 50 nm were continuously formed on the EML, which was thermally deposited at a rate of 0.2 nm / s under a base pressure of 2 × 10 ^-6 Torr. The active emission region between the electrodes of the device and ITO was 3 mm x 3 mm. To make green and red SM OLEDs, Ir (ppy) ₃ and Ir (piq) ₂ acac were added to the blue EL solution as green guest and red guest, respectively. Ir (ppy) ₃ and Ir (piq) ₂ acac were 0.15 and 0.07 wt% in green and red SM OLED, respectively. For comparison, a comparative device without a PTE additive was fabricated to investigate the EL performance of the device under study. The concentration of the PTE additive was 0.0 and 0.1 wt% in the blue SM OLED and 0.0 and 0.1 wt% in the comparative example B1 and the comparative example B2, respectively, in the comparative example G1 or R1 of the green and red elements and in the example G2 or R2, Respectively.

The characteristics are as follows.

The optical properties of the fabricated functional layers were investigated using a UV-visible spectroscopy system (8453, Agilent).

To see the surface morphology of the fabricated layers, the surface roughness levels of the layers were observed with AFM (AFM, Nanosurf easyscan 2 AFM, Nanosurf AG Switzerland Inc.). Current-luminance-voltage ( JLV ) characteristics and Commission

A Keithley source measurement unit (Keithley 2400) and a luminance meter (Chroma Meter CS-200, Konica Minolta Sensing, Inc.) were used to measure the Internationale d'clairage (CIE) colorimetric system. EL spectra were recorded using a spectrometer (Ocean's Optics) and emission characteristics were measured using an integrating sphere measuring system (LCS-100, SphereOptics Inc.). The device characteristics were performed at room temperature under an air atmosphere without encapsulation treatment.

Hereinafter, the experimental results and characteristics investigation will be discussed.

H-dip coated HIL and EML for solution process SM OLED

Figure 2 shows a photograph and a schematic illustration of the H-dip coating method used in the coating process of solution processable SM OLEDs. With the H- dip coating, the thickness of the layer is the capillary the value of the coating solution: Since increased in proportion to the _{(capillary number C a = μ U} / σ) (μ and σ indicates the viscosity and surface tension of each coating solution And U indicates the coating speed.) The thickness of the layer can be precisely controlled. The thin film thickness ( h ) of the H-dip coated layer is related to the drag-out problem proposed by Landau and Levich, namely C _a "1; h = k C _a ^2/3 R _d . Where R _d denotes the associated subsequent meniscus, and k is a proportional constant. The inventors first examined the thickness of the H-dip coated HIL and EML as a function of coating rate U and interval height h ₀ (FIG. 2 (a) and FIG. 2 (b)). As can be seen from the graph, the film thickness of the H-dip coated PEDOT: PSS layer showed a continuous increase from about 18 nm to about 58 nm when U increased from 0.25 to 2.0 cm / s for h ₀ of 0.5 mm, When h ₀ was 0.6 mm, the thickness was thicker as U increased. These results were consistent with the theoretical explanation for the drag-out problem (solid line in FIG. 2 (a)).

In addition, similar to polymeric PEDOT: PSS HIL, low molecular weight EMLs doped with PTE additives exhibited U and h ₀ dependent thicknesses within the observed range. It is therefore clear that H-dip coatings are able to precisely control the functional layer thickness of organic low molecules and polymers by using U and h ₀ as control variables in solution-processable OLEDs.

Next, the quality of the thin film of the low-molecular-weight EMLs doped with an interface control additive and H-dip coating is examined.

In order to investigate the thin film quality of the prepared low molecular weight EMLs, the surface roughness of the solution coated EMLs was observed using AFM. Figure 3 is a schematic diagram of a blue light emitting EMLs stacked on a flat substrate with TcTa: SPPO13: Firpic EML and TcTa: SPPO13: Firpic: PTE EML spin coated and H-dip coated EMLs ). As shown in the figure, when these solvents are used, thin films are formed which are not homogeneous and poor in both spin coating and H-dip coating processes, as reported in the prior art, because of their low ability to form thin films. The RMS surface roughness of EML prepared by spin coating was about 0.55 nm, and the RMS surface roughness of EMLs fabricated by single H-dip coating was about 0.33 nm. Particularly, the low-molecular EMLs fabricated by spin coating and H-dip coating showed very small pinholes defects ranging from sub-micron size to nanosize, which can lead to deterioration of device performance. In contrast, in the case of H-dip coated low molecular weight EMLs mixed with PTE additives, such thin film defects or phase separation did not occur (FIG. 3 (b) bottom). These observations showed that the topography of EMLs made with H-dip coating became more homogeneous with the introduction of PTE additive into EMLs, and the RMS surface roughness of PTE-doped EMLs made with H- Was relatively low (about 0.27 nm). Also, the surface roughness irradiated at different locations of the EML was the same for all of the irradiated layers. This uniformity was obtained because the conditions under which EMLs were formed were related to the surfactant response of the PTE additives, which is a different aspect from low molecular EMLs. Clearly different from H-dip coating of EMLs with PTE, spin coating of EMLs with PTE, even when using the same solution and PTE additive, showed many nano-sized pinhole defects and poor quality EMLs It needs to be watched. Thus, uniform and smooth EMLs, which are simply fabricated with a single H-dip-coating with TcTa: SPPO13: Firpic: PTE, are suitable for the fabrication of SM OLEDs in solution processes. In addition, multi-component EMLs are more convenient than H-dip coating processes using evaporation. Because the doping components of EMLs such as Firpic can be easily obtained by simply weighing in contrast to more complex co-evaporation.

TcTa: SPPO13: Firpic: Host with PTE: The characteristics of blue SM OLEDs with H-dip coating of guest EML are as follows.

Considering the impressive film quality of the low-molecular EMLs constructed using the H-dip coating, we fabricated blue SM OLEDs with EMLs of TcTa: SPPO13: Firpic with PTE interface-engineering additives. But the LUMO of SPPO13 higher than most of the reported electron transporting host material, electron injection to the SPPO13 from the Al cathode with Cs ₂ CO ₃ was and still insufficient, which the interface between the PTE additives introduced into the EML EML and the cathode ( Lt; / RTI > interface). In order to investigate the effect of the PTE additive on the device performance, a blue device (B2) was fabricated [ITO / PEDOT: PSS HIL / TcTa: SPPO13: Firpic EML doped with PTE / Cs ₂ CO ₃ / Al] Devices without PTE (B1) were also fabricated. In order to predict the device performance, JLV characteristics of H-dip-coated blue SM OLEDs B1 and B2 were investigated as shown in FIG. The slope of the JV curve between both 0 and 17.5 V for both blue SM OLEDs showed complete diode characteristics and H-dip coated functional layers. Also, what is clearly seen from the JLV curve (Fig. 4 (a) and (b)) is that it shows charge injection of 5 to 6 V or less, and a sharp increase in the JLV curve is observed over this interval.

For example, the operating voltage of reference blue OLEDs without PTE (B1) is about 8.0 V at a brightness of 100 cd / m ² , 9.75 V at 1,000 cd / m ² and 10,000 cd / m ² 13.75V. At that time, the brightness reached a peak at about 22,000 cd / m ² (at 17.5 V). The figure also shows that the blue EL brightness is clearly higher in the B2 device plus the PTE additives. The values are 8.0 V at 100 cd / m ² , 10.0 V at 1,000 cd / m ² , 10,000 cd / m < ² > In this experiment, the maximum brightness at 17.5 V reached about 25,600 cd / m ² . The increased EL brightness of B2 suggests that the excitons are efficiently produced following the introduction of PTE-doped H-dip coated EMLs, which increases the number of exciton recombinations emitted through the electron-hole balance of EMLs I guess. The onset voltage of the device (V _ON , the voltage at 1 cd / m ² ) is 5.0 V or less (B2), which is lower than those without the PTE added (B1, about 6.0 V). The lowered V _ON shows that the electron injection barrier is greatly reduced by the intervention of the PTE additives, presumably reducing the work function and contact resistance. A possible mechanism for the reduction of the barrier is the formation of an interfacial dipole layer at the cathode interface by interaction between Al and oxygen atoms in the PTE. The illustration in FIG. 4 (b) shows the normalized EL spectra at 1,000 cd / m ² obtained from blue SM OLEDs that do not have PTE additives in EMLs or have. As shown in the figure, only one dominant peak was observed at 475 nm in the two blue elements B1 (without PTE) and B2 (with PTE), corresponding to the emission from Firpic. This suggests that the introduction of simple PTE additives into low molecular blue EMLs does not affect the emission spectrum properties of blue SM OLEDs.

It is also interesting that the efficiency is much higher when PTE additives are used. In this case, the peak luminance efficiency (LE) was 12.0 cd / A and the peak power efficiency (PE) peak was 4.1 lm / W. This is mainly the result of the injection of electrons and hole blocking, which are the essence of the PTE at the negative electrode interface. Moreover, even at a brightness of 10,000 cd / m ² , the LE of B2 with PTE is still 9.8 cd / A, which is higher than that of B1 without PTE (8.6 cd / A), which means that when PTE additives are used, It is obviously remarkably improved. All these results clearly show that the device performance levels are significantly higher when using H-dip coated EMLs doped with PTE additives.

It should be noted that the blue SM OLEDs showed the best performance for 80 nm thickness and EML with a PTE concentration of 0.1 wt%. When the thickness of the EML and the PTE concentration were changed, the device performance started to deteriorate. The performance of the blue elements is summarized in Table 1. That is, Table 1 in FIG. 11 summarizes the performance of co-host (SPPO13: TcTa) guest-based SM OLEDs with or without interfacial control PTE additives.

Next, we fabricated and examined green SM OLEDs, which included a single H-dip of comixed guest phosphors of Firpic: Ir (ppy) ₃ with co-mixed TcTa: SPPO13 host and PTE additives Includes -coated EMLs. 5 is a green light-emitting TcTa: SPPO13: Firpic: of Ir (ppy) spin-coating, and a single H-dip coated (single H-dip-coated) the EMLs (thickness 80 nm) when ₃ does not have or has the PTE additives AFM Show morphology.

As shown in the figure, a small molecule of TcTa: SPPO13: Firpic: Ir (ppy) ₃ prepared by both spin coating and single H-dip-coated, similar to blue-emitting EMLs EMLs showed surface morphology with sub-micron-size pinhole defects and relatively high surface roughness (about 0.30 nm). These EMLs In contrast, H-dip-coated TcTc: SPPO13: Firpic: Ir (ppy) 3: PTE EMLs are showed the excellent thin film forming ability, a spin coating the TcTc: SPPO13: Firpic: Ir ( ppy) 3: PTE EMLs Still showed some sub-micron-sized defects. This investigation showed that the topographies of EMLs formed using a single H dip coating were homogenized along with the introduction of PTE additives to low molecular weight EMLs. The RMS surface roughness of the EMLs with PT-formed H-dip-coatings was about 0.26 nm and the surface roughness properties illuminated in different areas of the EMLs were found to be the same for the investigated layers.

Next, J- LV characteristics of H-dip-coated green SM OLEDs were investigated as shown in FIG. Similar to Blue SM OLEDs, the slopes of the JV curves of green SM OLEDs both exhibit the same diodic characteristics as the perfect H-dip-coated EMLs diodes. Also, it can be seen that the voltage injections from the JLV curves are below 4.5-5.0 V, and beyond this range, the JLV curves rise sharply. For example, single and 6.5 V when the operating voltage of the green SM OLED G1 with H-dip-coated EML is one brightness of ^{100cd / m 2, 1,000 cd /} m 2 indicates 8.3 V, and 10,000 cd / m ² day when 11.3 V. The maximum brightness was about 99,300 cd / m ² at 20.0 V. The figure also shows that the green EL brightness levels were significantly higher in the device with H-dip-coated EMLs (G2) where PTE additives were used. We achieved a peak brightness of 115,000 cd / m ² in an H-dip-coated G2 device, much higher than the G1, a device without PTE. In addition, in terms of efficiency, the use of H-dip-coated EMLs using PTEs was significantly higher. The overall performance of the G2 device was improved. The LE maximum value was 31.2 cd / A and the PE maximum value was 11.0 lm / W. At a brightness of 10,000 cd / m ² , the LE of the G2 device with PTE still reached 31.0 cd / A, which is higher than the value of the G1 device (25.1 cd / A). These results clearly show that the device drive level is much higher when H-dip-coated EMLs using PTEs are used. The illustration of FIG. 6 (b) shows the normalized EL spectra (at 1,000 cd / m ² ) obtained at G 1 and G ² , showing one dominant peak at 518 nm, ) _3. ≪ / RTI > Table 1 shows the performance of Green devices.

The inventors have also was prepared / study the red OLEDs SM, co-mixed TcTa: Firpic having SPPO13 host PTE and _{additives: Ir (ppy) 3: Ir} (piq) 2 acac of co-mixed phosphors of guest H-dip- coated EMLs were investigated.

Figure 7 shows AFM morphologies of spin-coated EMLs with and without PTE additives and single H-dip-coated EMLs (thickness 80 nm). As shown in the figure, low molecular EMLs of TcTa: SPPO13: Firpic: Ir (ppy) ₃ : Ir (piq) ₂ acac prepared by spin coating and single H-dip coating, similar to blue-emitting EMLs, showed pinhole defects of sub-micron-size and relatively high surface roughness (about 0.33 nm). In contrast to these EMLs, single H-dip-coated EMLs with PTE showed excellent film-forming capabilities and spin-coated EMLs with PTE still showed many sub-micron-sized defects. This investigation also showed that the topography of EMLs formed by H-dip-coating was more homogeneous with the doping of PTE additives to low-molecular EMLs. The RMS surface roughness of EMLs with PTEs fabricated using H-dip-coating was about 0.27 nm, and surface roughness properties in different areas of EMLs were found to be the same in the investigated layers.

We also investigated the JLV characteristics of H-dip-coated red SM OLEDs as shown in FIG. Similar to blue SM OLEDs, the slopes of the JV curves of the red SM OLEDs both show the perfect diode characteristics of H-dip-coated EMLs. In addition, a charge injection to 3.5 to 4.0 V or less from the J -LV curve outside this range can be clearly seen that they increase dramatically JLV curve. For example, the operating voltage of the red OLED SM R1 is 6.5 V, and, 1,000 cd / m ² when one 10.0 V, and 18.5 V when 10,000 cd / m ² day when the brightness of 100cd / m ^2. The maximum luminance was about 13,600 cd / m < ² > at 21.5V. This figure shows that the brightness level of the red EL is clearly higher in the R2 device in which the PTE additives are used. The peak luminance at R2 with PTEs was observed at 14,000 cd / m ² . This level is higher than R1 devices without PTEs. Also, the efficiency figures were also higher when H-dip-coated EMLs with PTEs were used. The R2 device showed good overall performance with a maximum LE of 4.0 cd / A and a maximum PE of 1.3 lm / W. Even at a brightness of 10,000 cd / m ² , the LE of R2 with PTEs was still 3.1 cd / A, which is higher than the value of the R1 element without the PTE additives (2.7 cd / A). The illustration of FIG. 8 (b) shows the normalized EL spectra obtained at R1 and R2. Here we can see that one dominant peaks was formed at 622 nm, corresponding to the emission from Ir (piq) ₂ acac. The drive values of the red devices are summarized in Table 1.

Referring to the above-mentioned H-dip-coated SMOLEDs device drive ( JLV ) data (FIGS. 4, 6 and 8) with PTEs, a single H- It can be clearly seen that dip-coated EMLs improve the EL efficiency characteristics of blue, green, and red EL emitters. Therefore, the use of H-dip-coated EMLs with PTE in solution process SM OLEDs is a reasonable choice for R, G and B color emissions because it provides high brightness and efficiency levels.

The following describes large-area H dip coated R, G, and B SM OLEDs.

Stimulated by impressive results from R, G, and B color SM OLEDs based on H-dip-coated EMLs with PTE, the present inventors found that a large 5 cm x 5 cm ITO- -area) SM OLEDs were fabricated by H-dip-coating method. This was done to evaluate the process suitability of SM OLEDs in a large-area solution process. A photographic image of the manufactured device is shown in Fig. 9 (a). Blue, green, and red EMLs were deposited horizontally on a glass substrate with a pixel size of 1 cm × 1 cm using H-dip-coating technique. Although the low-molecular EMLs with PTE additives treated with solutions in SM OLEDs were made entirely in air, the figure clearly shows that the produced SM OLEDs were fairly bright. In addition, the low change of the light emission intensity at the light emitting portion suggests that the change of the thickness of the EMLs coated by the solution process is small. In addition, the fact that the fluctuation of the EL intensity throughout this active region is small indicates that this method is suitable as a mass production method. The EL spectra collected from the pixels on the substrate were approximately the same as those shown in Figures 4, 6 and 8. Figure 9 (b) As shown in the blue-, green-, and red-emissive SM OLEDs has CIE coordinates of each (0.17, 0.40), (0.30, 0.63) and (0.60, 0.38) at 10,000 cd / m ² Demonstrating clearly how easy the introduction of H-dip-coated EMLs with OLEDs with PTEs into the production of full-color SM OLEDs can be used. These results demonstrate that H-dip-coated EMLs with PTE additives are easier to expand to larger sizes at lower cost than other processes and can provide an efficient manufacturing process.

Finally, we describe extending the self-metering coating mode to slot die coating to make SM OLEDs.

In order to confirm the possibility of extending the self-metered H-dip-coating mode with PTE additives to the slot-die coating, the present inventors have developed a commercially available 12 mm thick slot- (Test) blue SM OLEDs containing PTE additives and EMLs of TcTa: SPPO13: Firpic were prepared using a commercially available (FOM Technologies, shim-mask thickness = 1.0 mm) For slot-die coating, the coating gap was 0.5 mm and the coating speed was 1.9 cm / s. The dependence of the thickness of the self-metered slot-die coated layer on the coating speed and the gap height depends on the thickness of the H-dip-coated layers, ie the thickness of the EML layers, It is very similar to the steady increase in velocity U. In addition, when PTE additives were used, slot-die-coated TcTc: SPPO13: Firpic: PTE EMLs also exhibited excellent film forming capabilities without submicron size defects, EMLs (Figure 3). Details about the dependence of thin film thickness on U will be studied elsewhere. In order to confirm the performance of the device, as shown in FIG. 10, we investigated JLV characteristics for slot-die-coated blue SM OLEDs. The slope of the JV curve shows perfect diodic characteristics and shows good coverage of slot-die-coated layers (Fig. 10 (a)). It is also apparent that the charge injections in the J- LV curve (Figs. 10 (a) and (b)) are below 5 to 6 V, and the JLV curves increase sharply beyond this range. For example, the start of the slot-die-coated SM blue OLEDs with a PTE (ONSET) voltage is 5.5 V or less, and the operating voltage of the OLEDs is about 7.0 V when the brightness of ^{100cd / m 2, 1,000cd / m} 2 in the 8.25 V, and 11.75 V for 10,000 cd / m ² . The maximum luminance was about 25,000 cd / m ² at 16.0 V. Also, the efficiency was clearly high when using slot-die-coated blue EMLs with PTE. A peak LE of 14.5 cd / A and a peak PE of 5.3 cd / W were obtained in this experiment. Even in the light of 10,000 cd / m ² , the LE of the slot-die-coated blue SM OLED with PTE was still 13.3 cd / A.

The illustration in FIG. 10 (b) shows that for a slot-die coated blue element, only one dominant peak in the normalized EL spectra (1,000 cd / m ² ) is 475 nm Show what is observed. All of these results clearly demonstrate that the device performance of a slot-die coated blue device with PTE is similar to that of a H-dip-coated blue SM OLED with PTE (Fig. 4). This clearly indicates that the self-metered solution coating mode can be used extended with slot-die coating to produce low molecular weight films. Details of device performance will be announced elsewhere.

These observations suggest that a self-metered solution-coating process with a PTE additive promises a simplified production of flat, uniform, and confident low-molecular EMLs, which can be quickly processed, , Leading to the implementation of bright, efficient full-color SM OLEDs. In addition, solution process approach using self-metered coating mode is more convenient than using conventional vacuum evaporation in multi-component EMLs fabrication. This is because, unlike the conventional complex co-evaporation, the construction of the desired EMLs can be easily obtained by using appropriate weighting of the components. In addition, the performance of solution processable full-color SM OLEDs can be improved by adjusting host / guest materials and solutions, solution concentration, viscosity, gap height, and the like. In addition, the formation of other functional layers through self-metered H-dip coating and slot-die methods could be applied as a good advantage in fabricating new organic electronic devices.

In addition, the present invention can be applied to a roll-to-roll or the like, and can be applied to a display, an illumination, a photoelectric device, and the like.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are in all respects illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

Claims (1)

As SM OLEDs (small molecular organic light-emitting devices)
A transparent electrode, a transparent electrode, a positive electrode, a hole transporting layer, emission layers (EMLs), an electron injection interface layer,
The light-emitting layer comprises a mixed host: a doped guest (co-host: guest) based system,
PTE (polyoxyethylene (n) tridecyl ether) as a surfactant (interface-engineering additive) is contained in the light emitting layer in an amount of 1 wt% or less,
Wherein the OLED is formed by a solution coating method.

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