Mechanism study on highly efficient polymer light-emitting diodes utilizing double-layered alkali halide electron injection layer

Abstract

Enhancing the injection of electron is an effective strategy to improve the performance of polymer light-emitting diodes (PLEDs). In this work, we reported a 286% improvement in current efficiency (CE) of PLEDs by using double-layered alkali halide electron injection layer (EIL) NaCl/LiF instead of LiF. A significant enhancement of electron injection was observed after inserting the NaCl layer. To understand the mechanism of such improvement, the devices with KBr/LiF and CsF/LiF as EILs were also investigated. Experimental results show that metal cation migrated under the effect of built-in electric field (Vbi), which plays the main role on the improvement of electron injection in PLEDs.

Metal–Organic Framework for Efficient Electron Injection

“…On the other hand, the deposition of electron-injecting layer (EIL) with low work function is required for efficient electron injection from the Fermi level of the cathode into the lowest occupied molecular orbital (LUMO) of electron-transporting layer (ETL). Generally, interfacial materials such as reactive metals (e.g., Ca, Ba, or Mg), alkali metal compounds (e.g., LiF, Liq, CsF, or NaCl), [13][14][15] and n-type doped ETLs by alkali metal salts (e.g., Cs 2 CO 3 or Li 2 CO 3 ) [16,17] are inserted between cathode and ETL to achieve efficient electron injection. Recently, rare-earth metals (e.g., Yb) have also been reported as cathode interface layer (CIL) to improve the charge-carrier balance.…”