Tatsuo Mori

Electrical conduction behavior of organic light-emitting diodes using fluorinated self-assembled monolayer with molybdenum oxide-doped hole transporting layer

The electrical conductivity behavior of a fluorinated self-assembled monolayer (FSAM) of a molybdenum oxide (MoOx)-doped α-naphthyl diamine derivative (α-NPD) in organic light-emitting diodes (OLEDs) was investigated. The current density of the MoOx-doped α-NPD/FSAM device was proportional to its voltage owing to smooth carrier injection through the FSAM and the high carrier density of its bulk. The temperature-dependent characteristics of this device were investigated. The current density-voltage characteristics at different temperatures were almost the same owing to its very low activation energy. The activation energy of the device was estimated to be 1.056 × 10(-2) [eV] and was very low due to the inelastic electron tunneling of FSAM molecules.

Effects of Self-Assembled Monolayers with Fluorinated Alkyl Chain

The electrical characteristics of fluorinated self-assembled monolayers (FSAMs) in organic light-emitting diodes (OLEDs) were investigated according to the change in the lengths of their alkyl chains. As the number of fluorine atom increases, the device with long alkyl chain length allows the flow of a large amount of current because of the improved barrier height of the hole injection. However, the current efficiency under long alkyl chain length was decreased by the switched carrier balance. The device with the shortest FSAM alkyl chain length demonstrated an approximately 68% higher current efficiency than that with the longest alkyl chain length.

High Efficiency Organic Light-Emitting Diode by Ag Anode Technique

The characteristics of a Ag anode with molybdenum oxide (MoOx)-doped N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-1,4′-diamine (α-NPD) are reported. The current efficiency of devices with a Ag anode was achieved over 8.2 cd/A due to the microcavity effect. The current density of the device with a 25% concentration of MoOx was higher than those of a 10% concentration due to the improved charge transfer effect. The device of a Ag anode with a 25% concentration of MoOx indicated an approximate 227% higher current efficiency than that of an ITO anode with a 25% concentration of MoOx. The driving voltage of a Ag anode with a 25% concentration of MoOx was achieved at 4.4V with 10−2 A/cm2.

Enhancement of electron injection accompanied with the increase in hole injection for organic light-emitting diodes

In organic light-emitting diodes, the carrier recombination of electron-hole can occur efficiently using function-separated multilayer structures because of smooth carrier injection and transport. Therefore, hole-or electron-injection layers are widely used to enhance carrier injection from electrodes. In this study, we compared copper-phthalocyanine (CuPc), PEDOT:PSS, and fluorinated self-assembled monolayer (FSAM) as a hole-injection material. We used an aluminum quinolone (Alq3) and a distyryl derivative (DPVBi) as an emitting material. In the former, all hole-injection materials enhanced the device current and all efficiencies of luminance per current were same. But, in the latter, although all hole-injection materials enhanced the device current, the efficiency of luminance per current was different. This is because the electron current cannot keep pace against the increase in the hole current since the electron injection from the cathode into DPVBi and the electron transportation of DPVBi are poor. When the 10 nm-thick Alq3 layer was inserted between DPVBi and the cathode, the device current increased and the efficiency of luminance per current showed almost same behavior. These results showed the enhancement of electron injection accompaied with hole injection.

Effect of alkyl chain length of fluorinated self-assemble monolayer to organic light-emitting diodes as a hole injection layer

The introduction of fluorinated self-assembled monolayer (FSAM) enhanced hole injection from indium-tin-oxide (ITO) and improved device lifetime for organic light-emitting diodes. These effects were caused by the large dipole moment of FSAM molecule. We studied the effect of fluorinated alkyl chain length. Although the increase in alkyl chain let to the increase in dipole moment, it also meant the increase in insulating part. However, a small increase in alkyl chain did not influence the enhancement of hole injection from ITO. A short alkyl chain disturbed the regular formation of SAM by lowering an intermolecular interaction.

Electrical conduction of parylene composite thin films

Parylene (poly-p-xylene) is a famous heat-resisting polymer and its melting point is ~400°C. Especially Parylene is often used as a flexible sheet and encapsulation film of organic transistors and light-emitting diodes. However, Parylen has an interesting electrical behavior, the same negative temperature dependence of current as metals. In this report, the electronic states (HOMO and LUMO) of Parylene N are showed and the strange current behavior of the Parylene C/N and N/C bilayer films. The negative temperature dependence of current for the Parylene C/N (Parylene C on Parylene N) is 2-order stronger than that for a single Parylene N. On the other hand, the temperature dependence for the Parylene N/C (Parylene N on Parylene C) is positive but it shows smaller positive dependence than that for a single Parylene C. The current of Palylene thin film relates to electroluminescence (EL). It is reported that the EL is caused by the electronic avalanche, that is, an intrinsic EL. The EL of the Parylne bilayer films also depend on the amount of current. The top layer will control the carrier injection into the bottom layer and the divided voltage of the bottom layer.