Enhanced light extraction from organic light-emitting devices by using microcontact printed silica colloidal crystals

One simple method to increase the light extraction from organic light-emitting devices by using microcontact printed silica colloidal crystals is demonstrated. A close-packed hexagonal silica microsphere arrays is pressed into poly(vinyl alcohol) layer that is spin-coated on the opposite side of the indium–tin–oxide-coated glass substrate. This structure has the similar characteristics of microlens arrays. By using the silica microspheres with the diameters of 400 and 1000 nm those were half pressed into poly(vinyl alcohol), the luminance efficiencies of the devices in the normal direction are increased by a factor of 1.6 and 1.3 at the current density of 7.0 mA/cm2 compared to that of the device using flat glass substrate, respectively, and the shapes of emission spectra exhibit almost no angle dependence.