Designing an electron-transport layer for highly efficient, reliable, and solution-processed organic light-emitting diodes

We present solution-processable electron-transport layers (ETL) with highly enhanced electron-injection and electron-transport properties and resistance to oxygen and moisture for solution-processed organic light-emitting diodes (OLEDs). We selected polyethyleneimine ethoxylated (PEIE) as the ETL and Cs₂CO₃, CsF, and tris(8-hydroxyquinolinato)aluminum (Alq₃) as n-type dopants. Compared with OLEDs with undoped PEIE as the ETL, the OLEDs with doped PEIE (d-PEIE) showed significantly improved luminance, efficiency, and lifetimes. These improvements are attributed to d-PEIE decreasing the work function of the Al metal cathode, as shown by ultraviolet photoelectron spectroscopy (UPS) analysis, and improving the gas and moisture resistance.