Chemical changes on the green emitter tris(8-hydroxy-quinolinato)aluminum during device aging of p-i-n-structured organic light emitting diodes

Metal organic fluorescent and phosphorescent emitters are widely used in organic light emitting devices (OLEDs). Iridium-based triplet emitters are known to undergo chemical reactions with other materials during OLED aging. The material tris(8-hydroxy-quinolinato)aluminum (Alq(3)), which is widely used as electron transporting material and green fluorescent emitter, degrades mainly during hole transport. We investigate the chemical changes in Alq(3) during device aging: using laser desorption ionization time-of-flight mass spectrometry, we study the reaction products found in degraded OLEDs. Similar to the reactions known from the phosphorescent iridium-based emitters, Alq(3) undergoes a dissociation and further reaction with the hole blocking material 4,7-diphenyl-1,10-phenanthroline.