Fabrication of efficient polymer light-emitting diodes using water/alcohol soluble poly(vinyl alcohol) doped with alkali metal salts as electron-injection layer

An effective electron-injection layer (EIL) is crucial to efficient polymer light-emitting diodes (PLEDs) with high work-function metal as cathode. This work presents the use of water/alcohol soluble poly(vinyl alcohol) (PVA), especially doped with alkali metal salts, as a highly effective EIL to fabricate efficient multilayer PLEDs, allowing the use of stable aluminum as the cathode. Using neat PVA as EIL, the maximum brightness and maximum current efficiency of the device ITO/PEDOT:PSS/SY/PVA/Al(90 nm)] were significantly enhanced to 5518 cd/m² and 2.64 cd/A (from 395 cd/m² and 0.06 cd/A without the EIL) due to promoted electron-injection and hole-blocking. The device performance is further enhanced by doping the PVA with alkali metal salts (M₂CO₃ or CH₃COOM; M: Na, K, Cs), and the enhancement is increased with increasing dopant concentration. Particularly, the PVA doped with 30 wt% alkali metal carbonates revealed the best performance (20214–25163 cd/m², 5.83–6.83 cd/A). This has been attributed to improved electron-injection from aluminum cathode, which has been confirmed by the corresponding increase in the open-circuit voltages (V _oc) obtained from photovoltaic measurements. Current results indicate that commercially available PVA are promising electron-injection layer for PLEDs when doped with appropriate alkali metal salts.