Enhanced quantum efficiency in polymer light-emitting diode with water soluble non-conjugated polymer

We have fabricated highly efficient polymeric light-emitting diode (PLED) from water soluble non-conjugated polymer, polyurethane (PU), by using it as an ultra-thin insulating layer on the top of commercially available blue-emitting polymer, polyfluorene (PFO). The device with PU layer showed a maximum external quantum efficiency of 1.3% while the one without PU layer showed the efficiency of 0.6%. We propose that the better performance in PLED with PU layer was due to a well-balanced charge injection in emitting layer after the effective hole accumulation at the PFO/PU interface and thus increase in electron tunneling from cathode metal to emitting polymer.