Detection of Pre-electrical Breakdown of IZO/-NPD/Alq3/Al Light-emitting Diodes by Electric-field-induced Optical Second-harmonic Generation Measurement

By using the electric-field-induced optical second-harmonic generation (EFISHG), we measured the EFISHG-time (EFISHG-t) characteristics to study pre-electrical breakdown of indium-zinc-oxide (IZO)/ N,N'-di [(1-naphthyl)-N,N'-diphenyl]-(1,1'-biphenyl)4,4'-diamine (-NPD)/ tris(8-hydroxy-quinolinato)aluminum(III) (Alq3)/Al organic light-emitting diodes (OLEDs). A series of EFISHG pulses were identified as a pre-electrical breakdown phenomenon, before OLEDs were electrically broken. Analyzing the results revealed the additional negative charge accumulation at the -NPD/Alq3 interface which caused by the generation of EFISHG pulses. We concluded that the EFISHG-t measurement is available as a method for detecting pre-electrical breakdown phenomena of OLEDs.