Improved Hole-Blocking and Electron Injection Using a TPBI Interlayer at the Cathode Interface of OLEDs

The effect of a benzimidazole derivative (TPBI) electron injection layer (EIL) on the performance of Alq₃ based organic light−emitting devices (OLEDs) with a Cs₂CO₃/Al cathode is investigated. An increasing current density from 71.9 mA/cm² to 188.3 mA/cm², and an enhanced electroluminescence (EL) efficiency from 3.2 cd/A to 3.64 cd/A at 9 V are found when a thin TPBI layer (5 nm) is inserted at the Alq₃/Cs₂CO₃ interface. After further increasing the TPBI thickness to 10 nm, OLEDs display a further increase in EL efficiency to 4.53 cd/A. Our experiment suggests that the TPBI thin layer at the Alq₃/Cs₂CO₃ interface facilitates the electron injection and is also involved with hole-blocking and exciton confinement.