Real-time observation of temperature rise and thermal breakdown processes in organic LEDs using an IR imaging and analysis system

Real-time temperature measurements on green-emitting organic light-emitting diodes (OLED) consisting of a heterostructure of N,N′-diphenyl-N,N′bis(3-methylphenyl)-1,1′-biphenyl-4, 4′-diamine (TPD) and tris(8-quinolinolato) aluminum were performed using an infrared thermal imaging and analysis system. The thermal breakdown and surface temperature changes during the whole lifetime of OLEDs were investigated. The temperature rise due to the Joule heating effect inside the device was significant and higher than the glass transition temperature of TPD under a high forward-bias condition. The electric field-induced decomposition of indium tin oxide and electromigration of indium were responsible for the catastrophic failure or thermal breakdown of OLEDs.