Collaborative Research: Development of Dimeric Molecular n- and p-Dopants and their Application in Organic Light-emitting Diodes

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Non-Technical: There is increasing interest in low-cost, lightweight flexible electronic devices such as displays, lighting and solar cells that use organic (carbon-based) molecules or polymers in place of traditional semiconductors. The electrical properties of organic materials are often controlled using additives called dopants. The PIs have developed dopant molecules that exhibit an unprecedented combination of ease of use and effectiveness. Recently they have discovered that exposure to light can increase the utility of these dopants still further, enabling them to be used with materials suitable for display applications for which few other dopants are effective. This research explores the possibilities and limitations of this approach using chemical synthesis of new dopants, electrical measurements, and device fabrication and testing. Research outcomes may lead to improved devices, particularly displays that require less power. The research provides graduate students with interdisciplinary training, affords case studies for inclusion in the PIs' lectures, and gives opportunities for the education and training of women and minorities by hosting summer students and encouraging application to graduate school, recruiting at minority-serving institutions and conferences, and through interactions with New Mexico Highlands University.Technical: Controllable doping of organic semiconductors with molecular oxidants or reductants can greatly improve charge injection and conductivity in transistors (OFETs), as well as organic photovoltaics and light-emitting diodes. Dimeric n-dopants offer an unprecedented combination of ambient stability and strong reducing ability. This research builds on the PIs' recent findings that UV or visible light can extend the effective strength of these dimers beyond their thermodynamic limit, enabling n-doping of OLED materials. The goal of the research is to understand the mechanism, scope, practicalities, and limitations of the photoactivation, through varying the semiconductor electron affinity and rigidity, developing both stronger and weaker dimeric n-dopants, and developing dimeric p-dopants. The approach includes dopant synthesis and characterization; reactivity and photoactivation studies; electron spectroscopy, electrical, and dopant-diffusion measurements; and OLED fabrication and testing. Broader technological impacts include facilitating OLEDs with low turn-on voltages, and simplification of OPV and OFET manufacture. Educational impacts include interdisciplinary training of research students in synthetic chemistry, physical characterization, and device work; incorporation of materials based on the research into lectures at the PIs' institutions and at New Mexico Highlands University (where students also determine crystal structures of new compounds); and opportunities for the education and training of women and minorities.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.