Interchain and intrachain emission branching in polymer light-emitting diode doped by organic molecules

A blend of the polymer poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) and the electron-transport molecule tris-(8-hydroxyquinoline) aluminum (Alq3) has been investigated by means of electroluminescence and fluorescence spectroscopy, upon variation of the Alq3 content in the blend. A decreased interchain emission is observed upon increasing Alq3 content, due to lower packing of the MEH-PPV chains which leads to a reduction in the interchain interaction, excimer formation, and emission probability. A branching of MEH-PPV interchain and intrachain emissive contributions is clearly time resolved and analyzed as a function of the Alq3 content. At high doping concentration, direct emission from Alq3 molecules is observed.