High-current stressing of organic light-emitting diodes with different electron-transport materials

Abstract

We conducted accelerated reliability tests of electron-only devices (EODs) and organic light-emitting diodes (OLEDs) differing only in their electron-transport material (ETM). High current stressing of EODs at 50mA/cm2 showed that Bphen~Alq3>TPBi>TAZ in terms of intrinsic material stability. In addition, the lowest unoccupied molecular orbital (LUMO) level and electron mobility have been identified as two other key material factors affecting the degradation rate of OLEDs. TAZ has a low electron mobility, a LUMO level misaligned with the Fermi level of the cathode, and poor material stability, leading to extremely poor reliability of devices with a TAZ electron-transport layer (ETL). In contrast, the OLED with a Bphen ETL exhibited more stable operation and a 76× longer luminance lifetime. Due to its relatively high electron mobility and good stability as well as perfect energy level alignment with the cathode, Bphen has proven to be the most desirable ETM from the standpoint of OLED reliability.