Interfacial effects in polymer LEDs

A polymer LED in which the emitter layer was a blend of an alternating block copolymer and poly(N-vinyl carbazole) (PVK) was fabricated with intermediate hole transporting layers of polyphenylene vinylene (PPV). It was found that this provided greatly enhanced quantum efficiency, as expected, but also that the photoluminescent and electroluminescent spectral properties of the system were functions of the thickness of the PPV, which in certain cases contributed to the overall emission. From a detailed study of this effect it was concluded that radiative decay of surface or interfacially located excitons in PPV displayed a vibronic structure which differed from that produced by decay of excitons in the bulk. (C) 1998 Elsevier Science B.V.