Organic light-emitting devices based on vacuum-deposited poly(p-phenylene) thin film

Organic light-emitting device with poly(p-phenylene) (PPP) is prepared by vacuum deposition with various heating rates. The structure, morphology, photoluminescence (PL), electroluminescence (EL), and current (I)–voltage (V)–EL characteristics have been studied by IR spectroscopy, atomic force microscopy (AFM) and spectrofluorophotometer. The IR spectrum gave an evidence that the vacuum-deposited PPP (vd-PPP) chain involves 8–9 p-phenylene rings, which is known to be an effective conjugation length. The onset of the EL occurs at the electric field of about 7×107 V/m. I–V dependence fits very well with the Fowler–Nordheim (FN) tunneling formula. The results suggest that charge carrier injection is a tunneling process through an energy barrier of about 0.6–0.8 eV in ITO/PPP/Al devices.