A Blue Exciton-Polariton Organic Light-Emitting Device

1. A Blue Exciton-Polariton Organic Light-Emitting Device Scott Bradley, 6-1 (Electrical Engineering) Master’s of Engineering Thesis Proposal Images in this presentation are from: Laboratory of Organic Optics and Electronics

2. Introduction • Project Motivation • Background • Organic Light-Emitting Devices (OLEDs) • J-Aggregates of Cyanine Dyes • Resonant-Cavity OLED • Device Fabrication • Research and Resources • Experimental Methods • Timeline and Goals • Summary Laboratory of Organic Optics and Electronics

3. What is a Polariton? • Quasi-particle consisting of a photon and an exciton. • An exciton is an excited electron paired with a hole—excited state of a molecule. • Exciton and photon pass energy back and forth.

4. Project Motivation • Exciton-polariton OLEDs have potential in optics applications. • Existing work has established theory and created a red exciton-polariton OLED (J. Tischler). • Work on a blue exciton-polariton OLED would allow for more research in fabrication. Laboratory of Organic Optics and Electronics

5. electrons and holes form excitons (bound e--h+ pairs) _ E LUMO ETL HTL recombination region HOMO + some excitons radiate Background: Organic Light-Emitting Devices Example ETL Example HTL Laboratory of Organic Optics and Electronics

6. Background: J-Aggregates of Cyanine Dyes We use polar organic dye molecules… - + …which line up when deposited carefully… Called a J-Aggregate, named after Edwin Jelley of Kodak, who described the phenomenon in Nature in 1936. …and strongly absorb only one type of light.

7. Background: Resonant-Cavity OLED • Create a cavity tuned to the J-Aggregate absorption wavelength using silver mirrors. • Thin layers of silver are semi-transparent, so light is able get in and out of the cavity. Microcavity As long as the wavelength of light Laboratory of Organic Optics and Electronics

8. Device Fabrication: Dip-Coating J-Aggregate-Polyelectrolyte Bi-Layers Wavelength (nm) Fabrication Demonstrated Using Bi-Layer Deposition - Other J-Aggregates Likely Need Langmuir-Blodgett Absorption (Normalized) Programmable Slide Stainer(1) Wavenumber (cm-1) • Picture of Stainer from www.leica-microsystems.com • 400nm: Bucher, Kuhn, Chem Phys Lett 6 (1970) 183 • 465nm: Fukumoto,et al. Thin Solid Films 327–329 (1998) 748 • 550nm: Era, Adachi, Chem Phys Lett 178 (1991) 488 • 623nm: Rousseau, et al., Langmuir 16 (2000) 8865 • 890nm: Rotermund, et al. Chem Phys 220 (1997) 385

9. Research and Resources • Plan to use dye with absorption around 465 nm. • Process variation to improve fabrication: • pH variation of dye and polyelectrolyte solutions. • Dye concentration. • Number of layers. • Substrate variation (currently glass/ITO slides). • Different polyelectrolyte (currently PDAC). • Might change mirror from metal to dielectric Bragg reflector (DBR). • Planning to work with Prof. Vladimir Bulović. • LOOE has necessary fabrication equipment.

10. Experimental Methods • Electroluminescence measurements on patterned devices. [LOOE] • Photoluminescence measurements using 408 nm and higher energy lasers for excitation (fix excitation and scan through detection wavelengths). [LOOE] • Photoluminescence-excitation measurements (fix detection and scan through excitation). [other CMSE groups] • Reflection and transmission measurements using UV-Vis-NIR spectrometer. [CMSE Shared Analytical Lab]

11. Goals and Timeline Goals: • Build a blue exciton-polariton OLED. • Research fabrication process parameters. Timeline: • Currently doing related work in UROP position. • Be trained on necessary equipment by end of senior year. • Revisit M. Eng. thesis proposal and goals in spring 2004. • 6.728 in Fall 2004, 6.730 in Spring 2005. • Research process parameters to refine J-Aggregate bi-layer deposition with 465 nm dye (fall 2004). • Fabricate blue exciton-polariton OLED (spring 2005).

12. Summary • Blue exciton-polariton OLED fabrication and research could provide more information for further use of J-Aggregate-based devices. • Further understanding of deposition process could help in creation of J-Aggregated-based devices in NIR and IR.