Optical spectroscopy of triplet excitons and charged excitations in poly(p-phenylenevinylene) light-emitting diodes

Abstract

Sub-gap absorption is measured under forward drive conditions in electroluminescent devices fabricated from thin films of poly(p-phenylenevinylene) sandwiched between electrodes of indium/tin oxide and calcium. Quantitative concentrations of excitations are obtained. Absorption seen at 1.37 eV is due to an allowed transition to a higher-lying state of the excitons formed by capture of positive and negative charges in the polymer. Absorption bands at 0.65 and 1.55 eV are assigned to charged bipolarons which do not directly participate in the electroluminescence process. © 1993.