TITLE: Opto-electronic nanocomposites and the evolution of organic photonics

SPEAKER: Professor David L. Carroll,

TIME: Thursday Jan. 16, 2003 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Conjugated polymers are reaching commercial viability as the active layer in organic light emitting diodes (OLEDs), organic photovoltaics (OPV, solar cells), optical switches, thin film transistors, and more. However, their commercial application is hindered by shorter than desired efficiencies, reliabilities, and lifetimes. In this presentation, electro-active polymer - carbon nanotube "nanocomposites" will be introduced which hold tremendous promise in the creation of robust, high efficiency organic technologies. Single-walled carbon nanotubes (SWNT) dispersed into conjugated polymer hosts such as; poly(3-octylthiophene) (P3OT), poly(2-Methoxy-5-(2'-Ethyl-Hexyloxy)-p-PhenyleneVinylene) (MEH-PPV), and poly(9,9-dioctylfluorene) (PFO), modify photo-oxidation rates in the polymers through a suppression of triplet states, consequently enhancing device lifetimes fabricated from the composites. Incorporation of the SWNTs into OLEDs has shown remarkable benefits with regard to photo-oxidation of the polymer which also provides a reduction in the degradation of the polymer-metal interface during operation. This has led to much longer lived OLED devices. Surprisingly, however, the nanocomposite OLEDs also exhibit greatly enhanced efficiencies allowing for some of the brightest diodes yet created (> 35,000 Cd/m2). The benefits of SWNT nanocomposites in organic photovoltaics (OPV) are less clear. In some materials, such as P3OT, the incorporation of nanotubes improves the efficiency of the OPV through modification of the transport, but does not appreciably improve the donor-acceptor interface. In other polymer systems such as PFO, efficiencies of the nanocomposites are actually worse than those of the pure polymer. This can be fully understood in terms of a simple donor - acceptor model for the nano-dispersant in each system. This model strongly suggests that commercially realizable OPVs, OLEDS, and other high performance organic devices will require tailoring the nanotube electronics through doping. Recent progress in doping SWNTs and their use in nanocomposite applications will be presented.