Enhanced light extraction of organic light emitting diodes by embedding printed polymethyl methacrylate dot array

Inkjet-printed dot array structure embedded at the organic layer/ITO interface for enhancing out-coupling of OLED has been demonstrated. Polymethyl methacrylate (PMMA) which is transparent, cheaper and has refractive index (n= 1.47) similar to SiO₂ (n= 1.45), is selected as the dot array material. At the optimum period of 100 μm, the PMMA dot array improved the OLEDs current efficiency and power efficiency by the factors of 1.37 and 1.30, respectively. The current density and luminance of the device and light transmittance of different structure modified substrates have also been characterized to understand the improvement. The enhancement can be attributed to the light out-coupling of the printed dot array and the lower refractive index of PMMA material.