Organic light-emitting device

An organic light-emitting device includes a substrate, an anode including Ag on the substrate, a transparent inorganic thin-film layer on the anode, the transparent inorganic thin-film layer being in contact with the anode and having non-conductive characteristics; and an emitting layer and a cathode disposed sequentially on the inorganic thin-film layer.

This application claims priority from Korean Patent Application No. 10-2011-0044048 filed on May 11, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

Embodiments relate to an organic light-emitting device.

2. Description of the Related Art

An organic light-emitting device is a self-emitting display device including an anode, a cathode, and an organic film inserted between the anode and the cathode. When a current is supplied to the organic light-emitting device, the organic light-emitting device emits light by the combination of electrons and holes in the organic film. Accordingly, organic light-emitting devices make it possible to realize a lightweight, thin display device having high image quality, fast response time, and wide viewing angle characteristics. Currently, organic light-emitting devices are used not just in mobile phones, but in a wide range of applications including various high-definition information display devices.

SUMMARY OF THE INVENTION

According to one or more embodiments, an organic light-emitting device may include a substrate, an anode including Ag on the substrate, a transparent inorganic thin-film layer on the anode, the transparent inorganic thin-film layer being in contact with the anode and having non-conductive characteristics, and an emitting layer and a cathode disposed sequentially on the inorganic thin-film layer. The inorganic thin-film layer may have dipole characteristics. The inorganic thin-film layer may include Yb2O3. The inorganic thin-film layer may have an extinction coefficient value of 0.001 or less for light of wavelengths of 420 to 480 nm. The inorganic thin-film layer may include an In-containing oxide. The In-containing oxide may be InAsOx or InPOx.

The anode may be thicker than the inorganic thin-film layer. The inorganic thin-film layer may have a thickness of 10 to 200 Å.

The organic light-emitting device may further include a hole injecting layer, a hole transporting layer, and an electron transporting layer, wherein the hole injecting layer and the hole transporting layer are disposed sequentially on the inorganic thin-film layer, the emitting layer is disposed on the hole transporting layer, and the electron transporting layer and the cathode are disposed sequentially on the emitting layer. A contact surface of the inorganic thin-film layer in contact with the hole injecting layer may be uneven.

According to one or more embodiments, an organic light-emitting device may include a substrate, an anode including Ag on the substrate, a thin-film layer on the anode, the thin-film layer in contact with the anode, and an emitting layer and a cathode disposed sequentially on the thin-film layer, wherein the thin-film layer has an extinction coefficient value of 0.001 or less for light of wavelengths of 420 to 480 nm. The thin-film layer may include a transparent inorganic material having non-conductive characteristics. The thin-film layer may include at least one of Yb2O3, InAsOx, and InPOx. The thin-film layer may have dipole characteristics. The thin-film layer may have a thickness of 10 to 200 Å.

The organic light-emitting device may further include a hole injecting layer, a hole transporting layer, and an electron transporting layer, wherein the hole injecting layer and the hole transporting layer are disposed sequentially on the thin-film layer, the emitting layer is disposed on the hole transporting layer, and the electron transporting layer and the cathode are disposed sequentially on the emitting layer. A contact surface of the inorganic thin-film layer in contact with the hole injecting layer may be uneven.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an organic light-emitting device according to an exemplary embodiment will be described with reference toFIGS. 1 through 3.

FIG. 1illustrates a cross-sectional view of an organic light-emitting device according to an exemplary embodiment.FIGS. 2 and 3illustrate graphs showing the extinction coefficients of materials, which form thin-film layers of organic light-emitting devices, according to some exemplary embodiments, with respect to optical wavelength.

Referring toFIG. 1, the organic light-emitting device according to the current exemplary embodiment includes a substrate100, an anode110, a thin-film layer120, an emitting layer150, and a cathode170.

The anode110may be disposed on the substrate100. The anode110may contain Ag to increase its reflectance. That is, the anode110may be made of Ag.

The thin-film layer120may be disposed on the anode110. Specifically, the thin-film layer120may be disposed directly on the anode110, and may be in contact with the anode110.

In an implementation, the thin-film layer120may be a thin film made of a transparent inorganic material having non-conductive characteristics.

The thin-film layer120may include a transparent material that allows light incident from the emitting layer150and light reflected by the anode110to pass therethrough. The thin-film layer120may not conduct electricity even when a potential difference is created at both ends thereof. That is, the thin-film layer120may have non-conductive characteristics, i.e., insulating characteristics. In addition, the thin-film layer120may be an inorganic thin film made of an inorganic material.

A representative example of a suitable material that may be used to form the thin-film layer120, which has the above characteristics, is Yb2O3. Other examples of suitable materials include LiF and MgF2. However, embodiments are not limited to the above materials. Any suitable material can be used to form the thin-film layer120according to the current exemplary embodiment as long as the material exhibits all of the above-described characteristics.

According to the current exemplary embodiment, light efficiency may be improved in the organic light-emitting device including the thin-film layer120made of a transparent inorganic material having non-conductive characteristics.

Specifically, when the thin-film layer120disposed on the anode110has a high light-absorption rate, the anode110may have relatively low reflectance. The low reflectance of the anode110may increase the amount of light lost during resonance, thereby reducing the efficiency of the organic light-emitting device.

In particular, when the thin-film layer120has a high absorption rate at optical wavelengths (approximately 420 to 480 nm) in a blue visible light region, the light efficiency of the organic light-emitting device may significantly deteriorate. Therefore, to increase the light efficiency of the organic light-emitting device, the reflectance of an electrode (e.g., the anode110) may be increased by reducing the absorption rate of the thin-film layer120at the optical wavelengths (approximately 420 to 480 nm) in the blue visible light region.

When the thin-film layer120is made of a transparent inorganic material (such as Yb2O3, LiF, or MgF2) having non-conductive characteristics, and is positioned to directly contact a top surface of the anode110of the organic light-emitting device, its absorption rate at the optical wavelengths (approximately 420 to 480 nm) in the blue visible light region may be reduced. Thus, the reflectance of an electrode (e.g., the anode110) may be increased. This will be described in greater detail with reference to experimental examples.

The thin-film layer120of the organic light-emitting device, according to some exemplary embodiments, may have dipole characteristics. For example, the arrangement of molecules of the thin-film layer120may be changed by an electric field or a magnetic field. Accordingly, when the same voltage is applied to the thin-film layer120and a thin-film layer having conductive characteristics, the current density per unit area of the organic light-emitting device including the thin-film layer120may not be lower than that of an organic light-emitting device including the thin-film layer having the conductive characteristics. Therefore, the organic light-emitting device including the thin-film layer120may maintain the same injection characteristics as the organic light-emitting device including the thin-film layer having the conductive characteristics. The injection characteristics of the organic light-emitting device including the thin-film layer120having the dipole characteristics will be described in greater detail later with reference to the experimental examples.

Yb2O3may be used to form the thin-film layer120, since Yb2O3has the characteristics described above. Also, LiF or MgF2may be used to form the thin-film layer120, since LiF or MgF2have the characteristics described above.

The thin-film layer120of the organic light-emitting device, according to some other embodiments, may have an extinction coefficient value of 0.001 or less at the optical wavelengths (approximately 420 to 480 nm) in the blue visible light region. Accordingly, the light efficiency of the organic light-emitting device may be improved.

Specifically, as described above, the thin-film layer120, which has an extinction coefficient value of 0.001 or less at the optical wavelengths (approximately 420 to 480 nm) in the blue visible light region, may have a low absorption rate of light in the blue visible light region. The low absorption rate may increase the reflectance of an electrode (e.g., the anode110), thereby improving the light efficiency of the organic light-emitting device.

An example of a suitable material for forming the thin-film layer120may be an In-containing oxide. More specifically, a suitable material for forming the thin-film layer120may be, for example, InAsOx or InPOx.

InFIGS. 2 and 3, extinction coefficient values k of InAsOx and InPOx are illustrated. Referring toFIGS. 2 and 3, InAsOx and InPOx have an extinction coefficient value of 0.001 or less at optical wavelengths of approximately 420 to 480 nm. Therefore, an In-containing oxide, such as InAsOx or InPOx, may be used to form the thin-film layer120.

Further, LiF has an extinction coefficient of 2.6×10−8at an optical wavelength of 450 nm. Therefore, LiF may also be used to form the thin-film layer120.

A thickness T2of the anode110of the organic light-emitting device according to some other embodiments may be greater than a thickness T2of the thin-film layer120. Here, the thickness T2of the thin-film layer120may be about 10 to about 200 Å.

The thin-film layer120having a thickness of 200 Å or less (e.g., to about 10 Å) may not adversely affect the injection characteristics of the organic light-emitting device and may enable the organic light-emitting device to maintain optimal injection characteristics.

The thin-film layer120having a thickness of 10 Å or more (e.g., up to about 200 Å) may not affect the thin-film stability and reflection characteristics of an electrode (e.g., the anode110). Thus, the thin-film layer120may ensure the thin-film stability of the electrode and enable the electrode to maintain optimal reflection characteristics.

Referring back toFIG. 1, the emitting layer150, which emits light, and the cathode170may be disposed sequentially on the thin-film layer120.

In some embodiments, a hole injecting layer130, which facilitates injection of holes and a hole transporting layer140, which facilitates the transportation of holes from the anode110toward the emitting layer150, may be disposed between the thin-film layer120and the emitting layer150. In addition, an electron transporting layer160, which facilitates the transportation of electrons from the cathode170toward the emitting layer150, may be disposed between the cathode170and the emitting layer150.

The hole injecting layer130and the hole transporting layer140may be sequentially disposed on the thin-film layer120, and the electron transporting layer160may be disposed on the emitting layer150. The hole injecting layer130, the hole transporting layer140, and the electron transporting layer160may be responsible for the injection and transportation of holes and electrons. Although not shown in the drawings, the hole injecting layer130, the hole transporting layer140, and the electron transporting layer160, may be omitted as desired or may have a multilayer thin-film structure.

Hereinafter, an organic light-emitting device according to another exemplary embodiment will be described with reference toFIGS. 4,5A and5B.

FIG. 4illustrates a cross-sectional view of an organic light-emitting device according to another exemplary embodiment.FIG. 5Aillustrates an enlarged cross-sectional view of a region H1shown inFIG. 1.FIG. 5Billustrates an enlarged cross-sectional view of a region H2shown inFIG. 4. For simplicity, a description of elements and features substantially identical to those of the previous embodiment described above with reference toFIG. 1will be omitted, and differences between the current and previous embodiments will mainly be described.

Referring toFIG. 4, a contact surface of a thin-film layer120of the organic light-emitting device that is in contact with a hole injecting layer130may be uneven. According to some embodiments, the contact surface of the hole injecting layer130and the thin-film layer120, i.e., surfaces of the hole injecting layer130and the thin-film layer120that contact one another, may be uneven surfaces, i.e., surfaces that are not planar or level. In other words, an interface between the hole injecting layer130and the thin-film layer120may be uneven. The uneven contact surface may further improve the reflectance of an electrode (e.g., an anode110), thereby further improving the light efficiency of the organic light-emitting device.

More specifically,FIG. 5Aillustrates an optical path of reflected light L1of incident light L in a case where the contact surface of the hole injecting layer130and the thin-film layer120is planar.FIG. 5Billustrates an optical path of reflected light L2of incident light L in a case where the contact surface of the hole injecting layer130and the thin-film layer120is uneven.

Referring toFIG. 5A, when the contact surface of the hole injecting layer130and the thin-film layer120is planar, totally reflected light (indicated by a dotted line) may be generated at an interface between the hole injecting layer130and the thin-film layer120, due to the density difference between them.

Referring toFIG. 5B, when the contact surface of the hole injecting layer130and the thin-film layer120is uneven, an angle of incidence and an angle of reflection are changed at the interface between the hole injecting layer130and the thin-film layer120. Thus, the totally reflected light (indicated by the dotted line inFIG. 5A) is not reflected at the interface but enters the hole injecting layer130as indicated by a dotted line inFIG. 5B. Accordingly, the uneven contact surface of the hole injecting layer130and the thin-film layer may further improve the reflectance of an electrode (e.g., the anode110), thereby further improving the light efficiency of the organic light-emitting device.

Hereinafter, experimental examples will be described with reference toFIGS. 6 and 7, and characteristics of an organic light-emitting device according to exemplary embodiments will be described based on the experimental examples.FIGS. 6 and 7are diagrams illustrating characteristics of an organic light-emitting device according to exemplary embodiments.

Experimental Example

A thin film of Yb2O3was formed with a thickness of 70 Å on an anode made of Ag with a thickness of 1000 Å, and the resultant structure was used in an experimental group in a light reflectance experiment. In addition, a thin film of ITO was formed with a thickness of 70 Å on an anode made of Ag with a thickness of 1000 Å, and the resultant structure was used in a control group. The experimental group and the control group were compared with an anode which was made of Ag with a thickness of 1000 Å and on which no thin-film layer was formed.

The results of the reflectance experiment are illustrated inFIG. 6. Referring toFIG. 6, reflectance is highest across the entire wavelength region when no thin-film layer is formed on an anode (see ‘A’ inFIG. 6). However, thin-film stability may not be secured only with the anode made of Ag. As such, a thin-film layer may be required as described above.

When Yb2O3used to form a thin-film layer (see ‘B’ inFIG. 6) the reflectance characteristics across the entire wavelength region were higher than ITO (see ‘C’ inFIG. 6). In particular, the thin film of the experimental group had a lower absorption rate than that of the control group at wavelengths (approximately 420 to 480 nm) in a blue visible light region. Thus, the thin film of the experimental group increased reflectance of an electrode.

To see if the increased reflectance leads to improved light efficiency of an organic light-emitting device, an experiment was conducted on the light efficiency of the organic light-emitting device.

The results of the experiment on the light efficiency of the organic light-emitting device are shown in Table 1 below.

In Table 1, the converted efficiency denotes the efficiency of an organic light-emitting device in view of color coordinate deviations. As shown in Table 1, the efficiency of an organic light-emitting device (‘B’ in Table 1) including the thin-film layer, according to exemplary embodiments, is greater than that of an organic light-emitting device (‘C’ in Table 1) including the ITO thin-film layer, by approximately 10 to 15%.

Lastly, in order to identify injection characteristics, the current density per unit area of the organic light-emitting device including the thin-film layer, according to exemplary embodiments and that of the organic light-emitting device including the ITO thin-film layer were measured with respect to voltage. The results are shown inFIG. 7.

Referring toFIG. 7, the organic light-emitting device (see ‘B’ inFIG. 7) including the thin-film layer, according to the exemplary embodiments is not greatly different from the organic light-emitting device (see ‘C’ inFIG. 7) including the ITO thin-film layer, in terms of current density per unit area. In addition, they have substantially the same current density value per unit area at a voltage of approximately 2 V or higher. Therefore, it can be understood that the organic light-emitting device (see ‘B’ inFIG. 7) including the thin-film layer, according to the exemplary embodiments, is not inferior in injection characteristics to the organic light-emitting device (see ‘C’ inFIG. 7) including the ITO thin-film layer.

In an organic light-emitting device according to exemplary embodiments, the light reflectance of an electrode may be improved, and the improved light reflectance may have the effect of significantly improving the light efficiency of the entire organic light-emitting device. In particular, a thin-film layer included in the organic light-emitting device, according to the exemplary embodiments, may have a low absorption rate at optical wavelengths (approximately 420 to 480 nm) in a blue visible light region, thus improving the light reflectance of the electrode and the light efficiency of the organic light-emitting device.

The light efficiency of an organic light-emitting device may improve as the reflectance of an electrode having a reflection function increases. Embodiments provide an anode including a single film of Ag having high reflectance. The thin-film layer may increase the thin-film stability of the organic light-emitting device while improving light efficiency, due to its low light absorption rate. Embodiments provide an organic light-emitting device with improved light efficiency.

In addition, the thin-film layer of the organic light-emitting device may have dipole characteristics. Therefore, the thin-film layer may maintain the same injection characteristics as a thin-film layer having conductive characteristics.