D.K. Fu

Light-emitting devices based on pyridine-containing conjugated polymers

We report the fabrication of light-emitting devices based on several pyridine-containing conjugated polymers and copolymers in various device configurations. The high electron affinity of pyridine based polymers enables the use of relatively stable metals such as Al or even ITO as electron injecting contacts. Taking advantages of the better electron transport properties of the pyridine-containing polymers, we fabricate bilayer devices utilizing poly(9-vinyl carbazole) (PVK) as hole transporting/electron blocking polymer, which improves the device efficiency and brightness significantly due to the charge confinement and exciplex emission at the PVK/emitting polymer interface. The incorporation of conducting polyaniline network electrode to PVK reduces the device turn on voltage significantly while maintaining the high efficiency. The control of the aggregate formation in the polymer films by blending with insulating host polymers opens up the possibility of making voltage-controlled multi-color light-emitting devices.

Novel light-emitting diodes involving heterocyclic aromatic conjugated polymers

We report the fabrication and properties of three-, four-, and five-layer electroluminescent devices fabricated from light emissive N-based heterocyclic novel polymeric derivatives of PPP and PPV with which they are isoelectronic. They include poly(pyridine vinylene), (PPyV), and poly(2,5-dihexadecanoxy phenylene vinylene pyridyl vinylene), (PPV.PPyV). Some of the devices operate in both forward and reverse bias modes thus enabling operation in an ac mode. One type of device has the general construction: M/I/polymer/I/ITO where M equals Cu or Al, I equals polyaniline (emeraldine base, EB) or poly(3-hexylthiophene), (P3HT), and polymer equals PPV.PPyV. Under low frequency ac (sinusoidal) driving, light pulses with twice the driving frequency were observed in a device where M equals Al or Cu, I equals EB and polymer equals PPV.PPyV; and in a device where M equals Al, I equals P3HT and polymer equals PPV.PPyV. In the latter device the electroluminescence spectrum in the reverse bias mode differed from that in the forward bias mode. It was also shown that blends of PPyV in Nylon 6,6 exhibit a lower operating voltage than the pure polymer.

Novel light-emitting devices based on pyridine-containing conjugated polymers

We present novel light-emitting devices based on several pyridine-containing conjugated polymers and copolymers in various device configurations. The high electron affinity of pyridine-based polymers improves stability and electron transport properties of the polymers and enables the use of relatively stable metals such as Al as electron injecting contacts. Bilayer devices utilizing poly(9-vinyl carbazole) (PVK) as a hole-transporting/electron-blocking polymer show dramatically improved efficiency and brightness as compared to single layer devices. This is attributed to charge confinement and exciplex emission at the PVK/emitting polymer interface. The incorporation of conducting polyaniline network electrode into PVK reduces the device turn-on voltage significantly while maintaining the high efficiency. Two novel device configurations that enable the use of high work function metals as electrodes are pointed out.

Exciplex emission in heterojunctions of poly(pyridyl vinylene phenylenevinylene)s and poly(vinyl carbazole)

Abstract We present photoluminescence and electroluminescence spectra of heterojunctions formed from poly(vinyl carbazole) (PVK) and poly(pyridyl vinylene phenylene vinylene) (PPyVPV). Bilayers of PVK and PPyVPV show a photoluminescence peak which cannot be assigned to either the PVK or the PPyVPV layer. Absorption spectra show that the additional feature results from an exciplex at the bilayer interface. The electroluminescence spectrum from the heterojunctions is due to exciplex emission, with internal efficiencies of ~ 0.1–0.5%.