In this work, an improvement in light extraction efficiency from MDMO-PPV based OLEDs by using colloidal crystals is demonstrated. The optimal SiO₂ sphere diameter for the colloidal crystal was calculated by the Plane Wave Expansion Method (PWEM), taking into account the dispersion relation of the system formed by a face-centered cubic colloidal crystal (FCC) infiltrated within the luminescent polymer MDMO-PPV. The fabrication method of such a polymer layer with a photonic crystal beneath by spin coating was proved and patented. Therefore, devices with the structure ITO/PEDOT/MDMO-PPV+SiO₂ colloidal crystal/Ag were elaborated. Compared with standard OLEDs containing a single MDMO-PPV luminescent layer, the external quantum efficiency of devices modified with a colloidal crystal matrix within the MDMO-PPV layer shows a significant increment, as evaluated from the optical power as a function of applied bias for both kinds of devices.