Solid Lighting Core Technologies

Abstract

The overall objective of this project is to demonstrate an ultra-effective light extraction mechanism that can be universally applied to all top-emitting white OLEDs (TE-WOLEDs) and can be integrated with thin film encapsulation techniques. The scope of work proposed in this project includes four major areas: (1) optical modeling; (2) microlens and array fabrication; (3) fabrication, encapsulation, and characterization of TE-WOLEDs; and (4) full device integration and characterization. First , the light extraction efficiency in a top-emitting OLED with or without a microlens array are modeled using wave optics. Second , individual microlenses and microlens arrays are fabricated by inkjet printing of microdroplets of a liquid thiol-ene monomer with high refractive index followed by photopolymerization. Third , high efficiency top-emitting white OLEDs are fabricated, and fully characterized. Finally , optimized microlens arrays are fabricated on TE-WOLEDs with dielectric barrier layers. The overall light extraction efficiency of these devices, as well as its wavelength and angular dependencies, are measured by comparing the efficiencies of devices with and without microlens arrays. In conclusion, we have demonstrated the feasibility of applying inkjet printed microlens arrays to enhance the light extraction efficiency of top-emitting white OLEDs. We have shown that the geometry (contact angle) of the printed microlenses can be controlled by controlling the surface chemistry prior to printing the lenses. A 90% enhancement in the light extraction efficiency has been achieved with printed microlens array on a top-emitting white OLED, which can be further improved to 140% using a more close-packed microlens array fabricated from a molding process. Future work will focus on improvement of the microlens fabrication process to improve the array fill factor and the contact angle, as well as use transparent materials with a higher index of refraction. We will also further optimize the procedures for integrating the microlenses on the top-emitting white OLEDs and characterize the overall light extraction enhancement factor when the microlens array is attached.