Polymer light emitting diodes containing nanoparticle clusters for improved efficiency

We realized polymer light emitting diodes (PLEDs) containing oxidic nanoparticle clusters between the emission layer and the cathode. Different PLEDs with SiO2 and SiO2/TiO2 nanoparticle blends were fabricated and characterized by electroluminescence (EL) and photoluminescence (PL) measurements. We found that the incorporation of pure SiO2 leads to the most efficient devices boosting the efficiency up to a factor of about 4 at 60mA/cm2. Characterization shows that this is not a scattering effect but rather due to enhanced internal quantum efficiency. The underlying mechanism is attributed to the nanoparticles creating a randomly nanopatterned cathode layer which in turn increases the electric field at the organic–cathode interface and the electron injection.