Properties of Light-Emitting Diodes Fabricated from Self-Assembled Multilayer Heterostructures of Poly(p-pyridyl vinylene)

Abstract

Hetrostructure multilayer thin films of electroactive polymers such as protonated poly(p-pyridyl vinylene), PHPyV, and sulfonated polyaniline, SPAn, have been successfully fabricated via a process based on the spontaneous self-assembly of conjugated polyions on a substrate. The heterostructure thin films formed by these different polymers exhibited a perfectly linear relationship between the absorbance and the number of a SPAn/PHPyV bilayer, SPAn/PHPyV(b), deposited. A greenish-yellow electroluminescent (EL) diode utilizing an SPAn/PHPyV multilayer thin film, SPAn/PHPyV(m), has been produced, and the EL properties of this device are discussed. The EL emission of this device can be qualitatively interpreted in terms of a radiative recombination of the singlet polaron exciton formed by the injection of electrons and holes. The EL intensity of this light-emitting diode is weak. This result is discussed in terms of the quenching centers associated with cationic sites on PHPyV polymer main chain at the heterojunction. The Stokes shift due to the absorption and emission of a phonon is clearly observed in the EL spectrum of this device. A small shift between the EL and PL spectra of SPAn/PHPyV(m) is observed. It was assumed that the EL emission takes place in a narrow region at the interface while the PL emission probes the bulk of the film. The SPAn/PHPyV(b) (LED) emits yellow light, but SPAn/PHPyV(m) emits greenish-yellow light, and there is a slight shift between the two spectra of these devices. These results can be interpreted in terms of the confinement effect of carriers in the superlattice structure of the SPAn/PHPyV (m) system.