Water/alcohol soluble electron injection material containing azacrown ether groups: Synthesis, characterization and application to enhancement of electroluminescence

Using an environmentally stable metal as the cathode in a polymer light-emitting diode (PLED) is an essential requirement for its practical application. We present the preparation of a water/alcohol soluble copoly(p-phenylene) (P1) containing pendant azacrown ether and ethylene glycol ether groups as a highly efficient electron injection layer (EIL) for PLEDs, allowing the use of environmentally stable aluminum as the cathode. Multilayer PLEDs [ITO/PEDOT:PSS/PF-Green-B/EIL/Al] using P1 as EIL exhibit significantly enhanced device performance, particularly in the presence of K ₂CO₃ or Cs₂CO₃. The maximum luminous power efficiency and maximum luminance of the device with Cs₂CO ₃-doped P1 as EIL were enhanced to 9.16 lm W^-1 and 17050 cd m^-2, respectively, compared with those without EIL (0.16 lm W ^-1, 890 cd m^-2). The turn-on voltage was also significantly reduced from 5.7 V to 3.7 V simultaneously. The performance enhancement has been attributed to improved electron injection which has been confirmed by the rise in open-circuit voltage (V_oc) obtained from photovoltaic measurements. The incorporation of such an electron injection layer significantly enhances device performance for PLEDs with an environmentally stable metal as the cathode.