Excitonic singlet-triplet ratios in molecular and polymeric organic materials

A simple technique employing reverse bias measurements of photoluminescent efficiency is described to determine the excitonic singlet-triplet formation statistics of electroluminescent organic thin films. Using this method, the singlet fractions in thin films of two organic emissive materials commonly used in organic light emitting devices, tris (8-hydroxyquinoline) aluminum (Alq₃) and poly2-methoxy-5- (2-ethylhexyloxy) -1, 4-phenylenevinylene (MEH-PPV), are found to be (201) % and (204) %, respectively. Results are confirmed using a sensitive synchronous detection scheme. We discuss other measurements and the current understanding of exciton formation statistics in polymeric and small molecular weight organic electroluminescent materials.