Zenken Kin

Effects of CsF/Metal Interface on Electron Injection in Polymer Light-Emitting Diodes

The effect of electron injection in polymer light-emitting diodes has been investigated at the interface between the CsF layer and metals of the cathode. Efficient electron injection was achieved when the thickness of the CsF layer deposited on the organic layer was 1.5 nm. When the thickness of the MgAg layer deposited on the CsF layer was more than 1 nm, efficient electron injection was achieved. For the device with a 1.5-nm-thick CsF and a 1-nm-thick MgAg cathode, the deposition orders of CsF and MgAg were independent of efficient electron injection. That is, the coexistence of CsF and MgAg near the organic layer resulted in efficient electron injection. To achieve efficient electron injection, we found that was sufficient device performance was obtained when the surface of the organic layer with CsF was covered with approximately 25% MgAg.

Polymer Device of Poly(3-hexylthiophene) with a Cathode Fabricated from Silver Nanoparticles by Wet Processing

The fabrication and characteristics of a polymer device of poly(3-hexylthiophene) (PAT6) with a cathode fabricated from silver (Ag) nanoparticles were investigated. As the formation temperature is 210°C, the cathode electrode can be formed by wet processing on the organic layer with an amorphous carbon nitride buffer layer and a bank to prevent Ag nanoparticles from penetrating into the organic layer. The PAT6 device with a cathode fabricated from Ag nanoparticles shows a photo-response and a red emission in the reverse and forward bias regions, respectively. We demonstrated the possibility of a polymer photodiode and an organic light-emitting diode with a cathode utilizing Ag nanoparticles.

Study on Electron Injection of Phosphorescent Polymer Light-Emitting Diodes Utilizing CsF/Metal Cathode

The effect of electron injection in polymer light-emitting diodes based on the phosphorescent material of fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) devices with CsF/MgAg/Ag cathodes were investigated. The device with MgAg (1 nm)/CsF (3 nm)/Ag cathode showed almost similar current density-voltage-luminance characteristics to that with CsF (3 nm)/MgAg (1 nm)/Ag cathode. The existence of interface between the organic layer and Cs or CsF results in low turn on voltage. To achieve the efficient electron injection and the low turn on voltage, it is necessary to exist MgAg and CsF interface at the position of about 1 nm from organic layer. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The electron injection effects between devices with CsF and Cs are different. It is suggested that the dipole of CsF affect the efficient electron injection.

Organic photonic devices utilizing nano-structured materials

The characteristics of organic photonic devices with various kinds of geometrical nano-structures at the interface between organic materials, and also between the organic layer and metal electrode are investigated. A cutoff frequency of more than 20 MHz was observed for single-layer heterostructure organic photodetector (OPD) by applying a reverse bias electric field under the illumination of the red repetition pulse light. The mixed-layer heterostructure OPD with high photocurrent and high speed photoresponse is suitable for the application of optical link devices. An organic light-emitting diode (OLED) with a partial doping layer at the interface of heterostructure device can be expected to improve the modulation characteristics. The existence of interface between the organic layer and Cs or CsF results in low turn-on voltage for OLEDs. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The efficient electron injection and the low turn-on voltage result from the coexistence of MgAg and CsF at the position of approximately 1 nm from organic layer. The poly(3-hexylthiophene) device with a cathode fabricated from Ag nanoparticles shows a photoresponse and a red emission in the reverse and forward bias regions, respectively. We demonstrated the possibility of polymer OLEDs using a cathode fabricated from Ag nanoparticles by wet processing.