The term, organic electronic device, refers to a device which requires electronic charge exchange between an electrode and an organic material by using holes and/or electrons. The organic electronic device can be largely classified into two types according to its operational principle as follows. One type is an electronic device having a configuration in which an exciton is formed in an organic material layer by photons flown from an external light source into the device and the exciton is separated into an electron and a hole, the electron and the hole formed are transported to a different electrode, respectively and used as a current source (voltage source), and the other type is an electric device having a configuration in which holes and/or electrons are injected into an organic material semiconductor forming an interface with an electrode by applying a voltage or current to two or more electrodes to allow the device to operate by means of the injected electron and hole.
Examples of the organic electronic device comprise an organic light emitting device, an organic solar cell, an organic photoconductor (OPC) and an organic transistor, which all require a hole injecting or transporting material, an electron injecting or transporting material, or a light emitting material for driving the device.
Hereinafter, the organic light emitting device will be mainly and specifically described, but in the above-mentioned organic electronic devices, the hole injecting or transporting material, the electron injecting or transporting material, or the light emitting material functions according to a similar principle.
In general, the term “organic light emitting phenomenon” refers to a phenomenon in which electric energy is converted to light energy by means of an organic material. The organic light emitting device using the organic light emitting phenomenon has a structure usually comprising an anode, a cathode and an organic material layer interposed therebetween. Herein, the organic material layer may be mostly formed in a multilayer structure comprising layers of different materials, for example, the hole injecting layer, the hole transporting layer, the light emitting layer, the electron transporting layer, the electron injecting layer and the like, in order to improve efficiency and stability of the organic light emitting device. In the organic light emitting device having such a structure, when a voltage is applied between two electrodes, holes from the anode and electrons from a cathode are injected into the organic material layer, the holes and the electrons injected are combined together to form excitons. Further, when the excitons drop to a ground state, lights are emitted. Such the organic light emitting device is known to have characteristics such as self-luminescence, high brightness, high efficiency, low drive voltage, wide viewing angle, high contrast and high-speed response.
The materials used for the organic material layer of the organic light emitting device can be classified into a light emitting material and a charge-transporting material, for example, a hole injecting material, a hole transporting material, an electron transporting material and an electron injecting material, according to their functions. The light emitting materials can be divided into a high molecule light emitting material and a low molecule light emitting material according to the molecular weight thereof, and can be divided into a fluorescent material that is derived from a singlet excite state of electrons and a phosphorescence material that is derived from a triplet excite state of electrons according to the light emitting mechanism. In addition, the light emitting materials can be divided into a blue, green or red light emitting material and a yellow or orange light emitting material required for giving more natural color, according to a light emitting color.
Meanwhile, in the case of when only one material is used as the light emitting material, the maximum light emitting wavelength is moved into the long wavelength by the interaction between molecules, the color purity is reduced, or efficiency of the device is lowered by the light emitting reducing effect. Accordingly, a host/dopant system can be used as the light emitting material for the purpose of enhancing the color purity and the light emitting efficiency through energy transfer. It is based on the principle that if a small amount of a dopant having a smaller energy gap than a host which forms a light emitting layer is mixed with the light emitting layer, excitons which are generated in the light emitting layer are transported to the dopant, thus emitting a light having a high efficiency. Here, since the wavelength of the host is moved according to the wavelength of the dopant, a light having a desired wavelength can be obtained according the kind of the dopant.
In order to allow the organic light emitting device to fully exhibit the above-mentioned excellent characteristics, a material constituting the organic material layer in the device, for example, a hole injecting material, a hole transporting material, a light emitting material, an electron transporting material and an electron injecting material should be essentially composed of a stable and efficient material. However, the development of a stable and efficient organic material layer material for the organic light emitting device has not yet been fully realized. Accordingly, the development of new materials is continuously desired. The need to develop the above material is the same as the case of the above-mentioned other organic electronic devices.