Improved light extraction efficiency in organic light emitting diodes with a perforated WO3 hole injection layer fabricated by use of colloidal lithography.

We present an organic light emitting diode with a perforated WO3 hole injection layer to improve the light extraction efficiency. The two-dimensionally perforated WO3 layer was fabricated by use of colloidal lithography. The light extraction efficiency was improved due to Bragg scattering of waveguide modes and surface plasmon polaritons, and the operating voltage was also decreased. As a result, the external quantum efficiency and the power efficiency were increased as compared with those of conventional organic light emitting diodes without WO3 layer. The angular dependence of emission characteristics was investigated by measuring radiant intensity profiles for emission angles and azimuthal angles.