ORGANIC ELECTROLUMINESCENT DISPLAY AND METHOD OF MANUFACTURING THE SAME

An organic electroluminescent display includes a substrate, a first electrode on the substrate, an organic light emitting part on the first electrode and including organic members having a first polarity, a second electrode on the organic light emitting part, and an alignment layer. The alignment layer contacts the organic light emitting part between the first electrode and the second electrode, and has a second polarity opposite to the first polarity. The alignment layer aligns the organic members in the organic light emitting part.

This application claims priority to Korean Patent Application No. 10-2013-0074803, filed on Jun. 27, 2013, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are hereby incorporated by reference in its entirety.

BACKGROUND

The invention relates to an organic electroluminescent display and a method of manufacturing the same. More particularly, the invention relates to an organic electroluminescent display having an improved light-emitting capability and a method of manufacturing the organic electroluminescent display.

2. Description of the Related Art

In general, an organic electroluminescent display includes an anode, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer. The organic electroluminescent display displays an image using a light generated by holes and electrons, which are respectively provided through the anode and the cathode and recombined with each other in the organic light emitting layer.

As an alignment state of organic molecules improves (e.g., is more regular) in the organic light emitting layer, a mobility of the organic molecules is improved. In general, however, the organic molecules are randomly arranged in an organic layer of the organic light emitting layer in order to maintain a stable energy state. Therefore, there remains a need for an improved organic electroluminescent display including an improved mobility of organic molecules having a stable energy state.

SUMMARY

One or more exemplary embodiment of the invention provides an organic electroluminescent display having an improved light-emitting capability.

One or more exemplary embodiment of the invention provides a method of manufacturing the organic electroluminescent display.

An exemplary embodiment of the invention provides an organic electroluminescent display including a substrate, a first electrode, an organic light emitting part, a second electrode and an alignment layer. The first electrode is on the substrate. The organic light emitting part is on the first electrode and includes first organic members having a first polarity. The second electrode is on the organic light emitting part. The alignment layer contacts the organic light emitting part between the first electrode and the second electrode, and includes second organic members having a second polarity opposite to the first polarity. The alignment layer aligns the first organic members in the organic light emitting part.

An exemplary embodiment of the invention provides a method of manufacturing an organic electroluminescent display including forming an alignment layer including first organic members having a first polarity, on a substrate; providing second organic members having a second polarity opposite to the first polarity, to the alignment layer, to form an organic light emitting part including the second organic members on the alignment layer; aligning the second organic members in the organic light emitting part on the alignment layer; and forming a second electrode on the organic light emitting part. The second organic members are aligned by an attractive force generated between the alignment layer and the second organic members when the organic light emitting part is formed on the alignment layer.

According to one or more exemplary embodiment of the invention, the organic members (which may be otherwise referred to as organic molecules) of the organic light emitting layer are easily aligned using the attractive force and the ionic bond between the organic members of the alignment layer and the organic molecules of the organic light emitting layer while the organic light emitting layer is formed on the alignment layer, by providing the organic molecules of the organic light emitting layer to the alignment layer. Thus, the organic light emitting layer may have electrical characteristics within a crystalline structure and the mobility of the organic light emitting layer is improved, thereby improving the light emitting efficiency of the organic electroluminescent layer.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view showing an exemplary embodiment of a pixel of an organic electroluminescent display according to the invention.

Referring toFIG. 1, an organic electroluminescent display300includes a display substrate100, and an opposite substrate200facing the display substrate100. The opposite substrate200is coupled to the display substrate100to reduce or effectively prevent entry of humidity and gas (e.g., moisture and air) into the display substrate100from outside of the display substrate100. According to another exemplary embodiment, the opposite substrate200may be omitted from the organic electroluminescent display300. Where the opposite substrate200is omitted from the organic electroluminescent display300, a sealant layer (not shown) is provided on the display substrate100to cover the display substrate100, thereby reducing or effectively preventing entry of the humidity and gas into the display substrate100.

The display substrate100includes a substrate10which may be otherwise referred to as a base substrate, a thin film transistor TR, a first electrode E1, a color filter CF, a pixel definition layer PDL, an alignment layer20, an organic light emitting part ELP and a second electrode E2. In an exemplary embodiment, one or more of the aforementioned elements may be included in the display substrate100, and the reference numbers described above may refer to one or more of such elements. In the illustrated exemplary embodiment, the organic electroluminescent display300is a rear surface light emitting type, and thus light emitted from the organic light emitting part ELP travels to the outside of the substrate10after passing through the substrate10. To this end, the substrate10may include a transparent insulating substrate, e.g., a glass substrate, a plastic substrate, etc. In addition, when the substrate10includes one of the aforementioned materials such as to be the plastic substrate, the substrate10may have flexibility.

The thin film transistor TR is disposed on the substrate10and electrically connected to the first electrode E1, to switch a driving signal applied to the first electrode E1. The thin film transistor TR includes an active pattern AP, a gate electrode GE, a source electrode SE and a drain electrode DE.

The source electrode SE is physically and/or electrically connected to a driving signal line (not shown), through which the driving signal is transmitted, and overlapped with the active pattern AP. The drain electrode DE is overlapped with the active pattern AP and physically and/or electrically connected to the first electrode E1. Thus, when the thin film transistor TR is turned on, the driving signal is applied to the first electrode E1through the driving signal line and the thin film transistor TR.

In the illustrated exemplary embodiment, the active pattern AP includes a semiconductor material, e.g., amorphous silicon or crystalline silicon, but is not be limited thereto or thereby. In an exemplary embodiment, for instance, the active pattern AP may include an oxide semiconductor material, such as indium gallium zinc oxide (“IGZO”), ZnO, SnO2, In2O3, Zn2SnO4, Ge2O3, HfO2, etc., or a compound semiconductor material, such as GaAs, GaP, InP, etc.

A gate insulating layer L1is disposed between the gate electrode GE and the active pattern AP, and an inter-insulating layer L2covers the gate electrode GE to respectively insulate the gate electrode GE from the source and drain electrodes SE and DE. A planarization layer L3covers the thin film transistor TR, and a contact hole CH is defined extending through a thickness thereof. The first electrode E1is electrically connected to the drain electrode DE through the contact hole CH.

The first electrode E1is disposed on the planarization layer L3and serves as an anode. In addition, when the organic electroluminescent display300is the rear surface light-emitting type, the first electrode E1may be a transparent conductive layer, e.g., indium tin oxide, indium zinc oxide, etc.

The pixel definition layer PDL is disposed on the planarization layer L3and the first electrode E1. An opening is defined in the pixel definition layer PDL to correspond to the first electrode E1. The opened portion of the pixel definition layer PDL may expose a portion of the first electrode EL. Accordingly, the alignment layer20and the organic light emitting part ELP may be sequentially stacked on the first electrode E1in the opened portion of the pixel definition layer PDL.

The alignment layer20is disposed between the first electrode E1and the organic light emitting part ELP. An interface S1is defined between the alignment layer20and the organic light emitting part ELP, and the alignment layer20makes contact with the organic light emitting part ELP at the interface S1. The alignment layer20is charged to an electrical polarity different from the organic molecules of the organic light emitting part ELP to align the organic molecules of the organic light emitting part ELP. The alignment layer20will be described in detail with reference toFIG. 2.

The organic light emitting part ELP is disposed on the alignment layer20, and the second electrode E2is disposed on the organic light emitting part ELP to serve as a cathode. In the illustrated exemplary embodiment, the organic light emitting part ELP may include an organic light emitting layer. As an organic light emitting layer, holes provided from the first electrode E1are recombined with electrons provided from the second electrode E2in the organic light emitting part ELP, and thus the organic light emitting part ELP emits the light.

In the illustrated exemplary embodiment, the light emitted from the organic light emitting part ELP may be a white light. The organic light emitting part ELP has a single-layer structure (e.g., monolayer) having a continuous form, and is disposed over both a non-pixel area and a pixel area of the organic electroluminescent display300, but the structure of the organic light emitting part ELP should not be limited thereto or thereby. According to another exemplary embodiment, the organic light emitting part ELP may have a patterned shape (e.g., discontinuous form) in the pixel area and/or may have a multi-layer structure including a hole injection layer, an electron injection layer and the organic light emitting layer.

The color filter CF is disposed on the substrate10to filter the light emitted from the organic light emitting part ELP to be a color light. When the light emitted from the organic light emitting part ELP is the white light, the white light is converted to the color light by passing through the color filter CF, and the color light travels to the outside of the substrate10.

The second electrode E2is disposed on the organic light emitting part ELP. When the organic electroluminescent display300is the rear surface light-emitting type, the second electrode E2includes a conductive material having a reflectivity to the light, e.g., a metal material. Therefore, the light emitted from the organic light emitting part ELP is reflected by the second electrode E2and travels to the color filter CF.

In the illustrated exemplary embodiment, a protective layer150is disposed between the display substrate100and the opposite substrate200. The protective layer150includes a polymer, such as a polyimide resin, and reduces or effectively prevents entry of humidity and gas from into the display substrate100.

FIG. 2is a partially enlarged view of an exemplary embodiment of a first portion A1shown inFIG. 1.

Referring toFIG. 2, the interface S1is defined between the organic light emitting part ELP and the alignment layer20, and the organic light emitting part ELP makes contact with the alignment layer20at the interface S1. In the illustrated exemplary embodiment, the alignment layer20includes first organic members M1which may be otherwise referred to as first organic molecules, charged to a negative polarity. In one exemplary embodiment, for instance, the first organic molecules M1includes a negative ion functional group FG1, e.g., a carboxyl group, a sulfonic acid group, etc., and is charged to the negative polarity.

The organic light emitting part ELP includes second organic members M2which may be otherwise referred to as second organic molecules, charged to a positive polarity. In one exemplary embodiment, for instance, the second organic molecules M2includes a positive ion functional group FG2, e.g., an amino group, an imino group, etc., and is charged to the positive polarity.

According to the structure of the alignment layer20and the organic light emitting part ELP, the second organic molecules M2are ionic-bonded to the first organic molecules M1at the interface S1. Where the second organic molecules M2are ionic-bonded to the first organic molecules M1, a bonding force of the ionic bond acts along a direction slightly tilted with respect to a normal line direction of the interface S1, but the direction along which the bonding force of the ionic bond acts is substantially in parallel to the normal line direction of the interface S1. In addition, a position of the positive ion functional group FG2is uniform in each of the second organic molecules M2. Therefore, the second organic molecules M2bonded to the first organic molecules M1at the interface S1are aligned to the normal line direction. In detail, when each of the second organic molecules M2has a structure extended in a long axis direction AX1thereof and the positive ion functional group FG2is connected to an edge in the long axis direction AX1of the second organic molecules M2, the long axis direction AX1may be substantially in parallel to the normal line direction of the interface S1by the bonding force of the ionic bond. Accordingly, the second organic molecules M2may be aligned in the organic light emitting part ELP, in the direction substantially in parallel to the normal line direction of the interface S1.

Further, since each of remaining second organic molecules M2among the second organic molecules M2, which is not involved in the ionic bond, effectively has two different polarities in the long axis direction AX1due to the positive ion functional group FG2, the remaining second organic molecules M2may be aligned such that the long axis direction AX1thereof is also substantially in parallel to the normal line direction of the interface S1.

As described above, when the second organic molecules M2are aligned in the direction substantially in parallel to the normal line direction of the interface S1by the alignment layer20, the organic light emitting part ELP may have electrical characteristics within a crystalline structure. In more detail, the overlap between orbitals is increased since the second organic molecules M2are aligned in the specific direction (e.g., regularly arranged), and thus electrons easily move in the organic light emitting part ELP. This means that the mobility of the organic light emitting part ELP is improved by the alignment of the second organic molecules M2. Therefore, the light emitting capability, which is caused by the recombination of the holes and the electrons in the organic light emitting part ELP, may be improved.

FIG. 3a cross-sectional view showing another exemplary embodiment of a pixel of an organic electroluminescent display according to the invention. InFIG. 3, the same reference numerals denote the same elements inFIGS. 1 and 2, and thus detailed descriptions of the same elements will be omitted.

Referring toFIG. 3, an organic electroluminescent display301includes a display substrate101and an opposite substrate200, and the display substrate101includes an organic light emitting part ELF.

In the illustrated exemplary embodiment, the organic light emitting part ELF includes a hole injection layer HIL, a hole transport layer HTL, an organic light emitting layer EML, an electron transport layer ETL, and an electron injection layer EIL, which are sequentially stacked on a first electrode E1. In addition, a first alignment layer21is disposed between the first electrode E1and the hole injection layer HIL, a second alignment layer22is disposed between the hole transport layer HTL and the organic light emitting layer EML, and a third alignment layer23is disposed between the organic light emitting layer EML and the electron transport layer ETL.

In the illustrated exemplary embodiment, similar to the alignment layer20described with reference toFIGS. 1 and 2, each of the first, second and third alignment layers21,22and23includes a material charged to the negative polarity. Where each of the first, second and third alignment layers21,22and23includes a material charged to the negative polarity, the hole injection layer HIL includes organic molecules charged to the positive polarity, so that the ionic bond is induced at a first interface S10between the hole injection layer HIL and the first alignment layer21. Thus, as the second organic molecules M2(refer toFIG. 2), the organic molecules are aligned to a normal line direction of the first interface S10in the hole injection layer HIL, thereby improving the mobility in the hole injection layer HIL.

In addition, each of the organic light emitting layer EML and the electron transport layer HTL includes organic molecules charged to the positive polarity, and thus the ionic bond may be induced at a second interface S20and a third interface S30, respectively. Therefore, the organic molecules are respectively aligned to the normal line direction of the second and third interfaces S20and S30in the organic light emitting layer EML and the electron transport layer HTL, to thereby improve the mobility in the organic light emitting layer EML and the electron transport layer HTL.

In the illustrated exemplary embodiment, the first, second and third alignment layers21,22and23are included in the organic light emitting part ELP′, but an additional alignment layer may be disposed between the hole transport layer HTL and the hole injection layer HIL and/or between the electron transport layer ETL and the electron injection layer EIL.

FIGS. 4A to 4Fare views showing an exemplary embodiment of a method of manufacturing the organic electroluminescent display shown inFIG. 1.FIG. 4C and 4Dare partially enlarged views of an exemplary embodiment of a second portion A2shown inFIG. 4A.

Hereinafter, an exemplary embodiment of a method of forming the alignment layer20will be described in detail with reference toFIG. 4A. Referring toFIG. 4A, the thin film transistor TR, the color filter CF, the first electrode E1electrically connected to the thin film transistor TR, and the pixel definition layer PDL are formed (e.g., provided) on the substrate10. A liquefied material LM is provided to the substrate10using a nozzle NZ to form an alignment material layer (indicated by20inFIG. 4A) on the first electrode E1and the pixel definition layer PDL.

In the illustrated exemplary embodiment, the liquefied material LM is manufactured by melting a solid material including the first organic molecules M1(refer toFIG. 2) charged to the negative polarity in solvent, and the liquefied material LM is provided to the substrate10using an inkjet method or a slit coating method. In addition, after the liquefied material LM is provided to the substrate10as the alignment material layer, a heat-treatment process is performed on the substrate10to remove the solvent from the liquefied material LM to form the alignment layer20.

Referring toFIG. 4B, the substrate10including the alignment layer20thereon (refer toFIG. 4A) is indicated generally as10, and is placed on a substrate supporter50in a chamber CB. The alignment layer20(refer toFIG. 4A) formed on the substrate10is exposed to a reaction space RS of the chamber CB while the substrate10including the alignment layer20thereon is supported by the substrate supporter50.

The reactive space RS is maintained in a vacuum state by using a vacuum pump (not shown) connected to the reactive space RS, and a deposition source SR disposed on a bottom portion of the chamber CB is heated. The deposition source SR may include a source material and the second organic molecules M2. The deposition source SR is manufactured by using the organic material including the organic molecules charged to the positive polarity in a power shape. When the deposition source SR is heated, the source material in the deposition source SR is evaporated and the second organic molecules M2exit from the deposition source SR. As a result, the second organic molecules M2exiting from the deposition source SR are provided to the substrate10after passing through the reactive space RS, and the second organic molecules M2are deposited on the alignment layer20(refer toFIG. 4A) formed on the substrate10, thereby forming the organic light emitting part ELP (refer toFIG. 1).

Hereinafter, an exemplary embodiment of a process of forming the organic light emitting part ELP will be described in detail with reference toFIGS. 4B,4C,4D and4E.

Referring toFIGS. 4B and 4C, the alignment layer20formed on the substrate10is exposed to the reactive space RS and the second organic molecules M2exiting from the deposition source SR travel toward the substrate10after passing through the reactive space RS.

As described above, although the second organic molecules M2are charged to the positive polarity, the second organic molecules M2may randomly exist in the reactive space RS as illustrated inFIG. 4Csince any element that causes an electrical operation with respect to the second organic molecules M2does not exist in the reactive space RS.

Referring toFIGS. 4B and 4D, when a portion of the second organic molecules M2reaches the alignment layer20, an attractive force occurs between the negative ion functional group FG1of the first organic molecules M1and the positive ion functional group FG2of the second organic molecules M2. As a result, due to the attractive force, the second organic molecules M2are aligned to allow the positive ion functional group FG2to face the negative ion functional group FG1, and the second organic molecules M2are ionic-bonded to the first organic molecules M1at the interface51between the alignment layer20and the organic light emitting part ELP.

Accordingly, the second organic molecules M2are deposited on the alignment layer20to form the organic light emitting part ELP and the interface51is defined between the organic light emitting part ELP and the alignment layer20. The second organic molecules M2are aligned at the interface S1along the normal line direction of the interface S1. These second organic molecules M2aligned at the interface S1may be otherwise referred to as base or initial second organic molecules M2.

Referring toFIGS. 4B and 4E, further second organic molecules M2are deposited on the initial second organic molecules M2ionic-bonded to the first organic molecules M1at the interface

S1, to continue forming the organic light emitting part ELP by deposition. Since each of the second organic molecules M2effectively has two different polarities in the long axis direction by the positive ion functional group FG2, the further second organic molecules M2are aligned such that the long axis direction of the further second organic molecules M2is substantially in parallel to the normal line direction of the interface S1while forming the organic light emitting part ELP proceeds.

Referring toFIG. 4F, once the organic light emitting part ELP is formed by depositing the second organic molecules M2(refer toFIG. 4B) on the alignment layer20(refer toFIG. 4A), the second electrode E2is formed on the organic light emitting part ELP, thereby manufacturing the display substrate100.

The protective layer150(refer toFIG. 1) is formed to cover the second electrode E2, and the opposite substrate200(refer toFIG. 1) is coupled to the display substrate100while interposing the protective layer therebetween, to thereby manufacture the organic electroluminescent display300(refer toFIG. 1).

FIG. 5is a cross-sectional view showing another exemplary embodiment of a method of forming the alignment layer with respect toFIG. 4Aaccording to the invention.

Referring toFIG. 4AandFIG. 5, the liquefied material LM includes non-polarity molecules, and is provided onto the substrate10using the spin coating method or the slit coating method to form a preliminary alignment layer20′.

Then, a light LT having energy greater than ionization energy of the non-polarity molecules, e.g., a laser beam, is irradiated onto the preliminary alignment layer20′. By irradiating the light LT onto the preliminary alignment layer20′, the non-polarity molecules of the preliminary alignment layer20′ absorb the energy of the light LT to discharge electrons, thereby forming the alignment layer charged to the positive polarity.

As described above, when the alignment layer charged to the positive polarity is formed, the organic molecules of the organic light emitting part ELP are charged to the negative polarity in order to induce the ionic bond between the molecules of the alignment layer and the organic molecules of the organic light emitting part ELP (refer toFIG. 1).

The method of charging the alignment layer to have the electrical polarity should not be limited thereto or thereby. In one exemplary embodiment, for instance, the alignment layer may have a positive or negative electrical property using an ion injection method.

Although exemplary embodiments of the invention have been described, it is understood that the invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the invention as hereinafter claimed.