HIGHLY EFFICIENT ELECTROLUMINESCENCE OF NEW WIDE-BAND GAP LADDER-TYPEPOLY(PARA-PHENYLENES)

We present the optical and electronic properties of a polymeric semico nductor, a new soluble stable ladder-type poly(para-phenylene) (LPPP, band gap=2.69 eV) and demonstrate its excellent applicability in blue- green electroluminescence (EL) devices. The high intrachain order and the low defect concentration of the polymer lead to a remarkably low a bsorption coefficient in the subgap region (alpha(min)<12 cm(-1) at 1. 5 eV) and also to a high photoluminescence quantum efficiency (30% in the solid state). The current/electric field characteristics of the hi gh efficiency (up to 0.04 photons/electron) EL devices reveal a polyme r film thickness dependence on the required onset field due to orderin g effects in the active polymer layer. The shape of the recorded EL sp ectra can be controlled by the applied electric field in the blue-gree n spectral range. (C) 1996 American Institute of Physics.