EAGER: Distributed Feedback/Distribute Gain Fabry-P?rot Microcavities for Organic Light Emitting Diodes

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

Nontechnical: Organic semiconductors are a novel class of materials with attractive properties such as low-cost processing and flexibility. This has led to the widespread adoption of organic light-emitting diodes (OLEDs) into displays for mobile phones and TVs. One important application, however, has not been possible: lasers. This project will lay the foundations for electrically-driven organic lasers by investigating the interaction of light and matter in periodic optical microstructures. A series of mirrors will create a distributed optical structure that only allows certain colors of light to pass through at specific angles. These mirrors will also function as the electrodes for OLEDs, confining light emission to specific locations within the mirror structure. The team will combine modeling with device fabrication and characterization to determine the effect of the optical microstructure on light emission. The project will push the combination of materials and device structure toward the lasing threshold. The project will also produce a publicly-available database of optical and electronic properties of materials for research and development. A summer workshop on organic optoelectronics will be organized, providing hands-on experience for high school STEM students to explore a cutting-edge research field. Technical: Electrically-pumped organic diode lasers offer immense potential and remain one of the major unsolved challenges in organic optoelectronics. Microcavity geometries show significant promise in optically-pumped systems, yet low carrier mobility and optical losses prevent devices based on organic light-emitting diodes (OLEDs) from approaching the lasing threshold. This project uses a distributed feedback and distributed gain geometry, decoupling the electrical transport from the optical path length. The electrical conduction occurs through only 100 nm of the OLED thickness, while the functional optical path length may be many orders of magnitude higher, depending on the number of stacked layers and the reflectivity of the mirrors. Standing-wave modes with nodes at the mirror surfaces minimize optical losses. The corresponding antinodes at the emission layer maximize the possibility of stimulated emission. Multiple modeling techniques will be used to optimized the microcavity design, driven by feedback from angle-resolved electroluminescence spectra of fabricated devices. The project will first explore the effects of cavity thickness and emitter position within the cavity for single-layer devices spanning multiple half-wavelength modes. The feedback mechanism and gain medium will then be distributed over multiple stacked devices, targeting the half-wavelength mode with resonance coincident with the electroluminescense peak of a given emitter molecule. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.