Photoluminescence and electroluminescence investigations in PEPPV and its derivatives

We report investigations of photoluminescence (PL) and electroluminescence (EL) in several derivatives of polyether–polyphenylenevinylene copolymer (PEPPV). PL spectra depend on the conjugated block lengths on the end group, chlorine or bromine. Electroluminescent diodes were built in the classical sandwich structure, by evaporating PEPPV and aluminium layer under vacuum on an indium–tin oxide-covered glass slide. EL is obtained at a low voltage (less than 4 V) and the diode quantum efficiency depends strongly on the applied voltage. Transient behaviour of PEPPV thin films devices was also investigated. Between the application of a short rectangular voltage pulse and the onset of EL, a time lag exists that is attributed to the mobility of the charge carriers.