Shuji Doi

Recent progress of high performance polymer OLED and OPV materials for organic printed electronics

Abstract The development of organic printed electronics has been expanding to a variety of applications and is expected to bring innovations to our future life. Along with this trend, high performance organic materials with cost-efficient fabrication processes and specific features such as thin, light weight, bendable, and low power consumption are required. A variety of organic materials have been investigated in the development of this field. The basic guidelines for material design and the recent progress of polymer-based organic light-emitting diodes (OLEDs) and organic photovoltaic cells (OPVs) are reported.

Organic electroluminescent devices having poly(dialkoxy-p-phenylene vinylenes) as a light emitting material

Abstract We have successfully prepared organic electroluminescent, EL, devices having poly(2,5-dialkoxy-p-phenylene vinylene)s, RO-PPV, as light emitting materials, ITO as a transparent electrode and Mg-Ag alloy as a negative electrode. Intensities of photo-, PL, and electro-luminescence for RO-PPVs depended on the chain length of alkoxy side groups. The PL intensity of the RO-PPV increased with increasing the alkoxy chain length, while the EL intensity of the devices using RO-PPV increased until a decyloxy group and then decreased. The EL intensity of the device increased with decreasing the work function of negative electrodes. This result is in good agreement with that reported by Heeger[5]. The luminance reached about 1000cd/m 2 by using both heptyloxy-PPV and MgAg alloy. It is noteworthy that usage of poly(thienylene vinylene), PTV, thin film as a buffer layer between ITO and RO-PPV results in increasing the breakdown voltage and that the luminance of the EL device reaches 1480 cd/m 2 .

Light-emitting polymers and their LED devices

Highly luminous polymers have successfully been prepared by copolymerization of various arylene vinylene units. The random copolymerization of the monomers having different energy gaps or conjugation degrees can generate the irregularity in poly(arylene vinylenes) and enhance the fluorescence of the polymer. Among the copolymers synthesized, the m/p-phenylene vinylene copolymer showed fairly strong fluorescence and gave the most efficient polymer light-emitting diode (P-LED) device because of the good balance of the exciton confinement and the charge transporting property. The optimized P-LED device showed a maximum luminance of 70000 cd/m/sup 2/.

Novel blue light-emitting polymers for PLED

We have been researching blue-emitting polymers and developed some novel polymers with blue fluorescence, which are not fluorene copolymers. Our previous works showed the dependence of EL efficiency on molecular weight of poly(p-phenylene vinylene) derivatives. We concluded that polymers must be synthesized by the method which gave larger molecular weight in order to achieve higher performance. Firstly, we modified the synthetic method of polyarylenes and confirm that Mw of ca.1,000 to over 1,000,000 is obtainable depending on the condition. Polymers having moderately large Mw showed good solubility in solvents and film-forming properties. PLEDs using these polymers had longer lifetime as well as higher EL efficiency. Secondly, we understood the importance of charge balance between electrons and holes, by using polyfluorene derivatives as model polymers. We measured electron, hole and total currents by electron-only, hole-only and usual bipolar devices respectively. We found out that the hole mobility could be changed from 10-7cm2/Vs to 10-3cm2/Vs depending on the content of hole transporting units. In addition, electron injection from a cathode seemed to be assisted by trapped holes. We utilized these results in order to design our blue polymers. Finally, we obtained a new blue-emitting polymer, which showed longer device lifetime among non-fluorene polymers.

Polymer light-emitting diodes utilizing poly(phenylene vinylene)derivatives

Abstract We have successfully synthesized highly luminous poly(phenylene vinylene) derivatives. The polymer having m-phenylene vinylene units showed good electroluminescent properties due to the good balance between the exciton confinement and the charge transporting property. The optimized P-LED, having a multi-layer structure, showed a maximum luminance of about 70,000cd/m 2 and a service life of over 1,000 hours

Polymer LED Utilizing Poly(arylene vinylenes)

Polymer light emitting diode, P-LED, has successfully been fabricated using highly luminous poly(arylene vinylene) derivatives. The P-LED showed a maximum luminance of 55,000cd/m2. This high performance of the device was achieved by employing copolymers of arylene vinylene units as a light-emitting material and a multi-layer structure for the device.