Ideal microlens array based on polystyrene microspheres for light extraction in organic light-emitting diodes

Ideal microlens array (IMLA) based on polystyrene (PS) microspheres with small diameters has been introduced to the surface of indium tin-oxide (ITO) glass substrates to enhance the out-coupling efficiency of organic light-emitting diode (OLED) devices. IMLA was fabricated by a replica molding process using annealed closely packed PS spheres as the template. IMLA is used to extract the waveguide mode which is limited in glass substrate. Experiment results show that the best performance of OLED devices is achieved when the diameter of IMLA is about 6 mu m. The enhancement of current efficiency, power efficiency and EQE of green-emitting OLED devices with IMLA with a diameter of 6 mu m is 56.4%, 63.5% and 58.8%, respectively, relative to devices without any light out-coupling structures in the forward direction. In addition, we also demonstrate that the IMLA with a diameter of 6 mu m can also be applied for the extraction of red, blue and white light. Furthermore, the use of IMLA is not detrimental to the electrical and optical performance of the OLED devices.