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Design and Deposition of Electroactive Polymers for Light-emitting Diodes and

Photovoltaics: DMR-0208786Mary Galvin, University of Delaware and Lewis Rothberg, University of Rochester

Goals: The goal of this research is to develop a model that explainswhy a mixture of conjugation lengths in a polymer affects the amount

of light emitted by light-emitting diodes (PLEDs).Research: Our past work has showed that polydispersity ofconjugation lengths can dramatically impact the efficiency of organic

LEDs fabricated from polyparaphenylenevinylenes. To explain the

impact, we have modeled these effects using a detailed quantitative

theory that takes into account trapping effects on charge transport,

charge injection and the location of the recombination region.

Experiments were performed by deliberate engineering of trapdistributions in organic LEDs fabricated from blends of conjugated

oligomers and polymers synthesized in the Galvin group. Theory was

done by modifying code written in collaboration with Darryl Smith at

Los Alamos National Labs. The result is a general theory that provides

a cost-benefit analysis for reducing polydispersity and extrinsic traps

in polymer light-emitting diodes. Given a materials electron and hole

mobilities plus HOMO and LUMO levels, the theory allows device

engineers to optimize contact selection and trap density. We have now

shown experimentally that traps can either increase or decrease

device efficiency.

NN

O

C8H17O

H3C

OC8H17

OC8H17

CH3

C8H17O

Oxadiazole pentamer

NN

O OC12H17

C12H17O

( )

OXAPPV

n

Fig. 1. Chemical structure of some of polymers and oligomers used to test model.

Fig. 2. (a) Model energy level scheme of a PPV-

oxadiazole pentamer Device with long chains blended

in. Internal quantum (b) and power (c) efficiency versuscurrent for various trap depths at 0.5% trap

concentration.

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Design and Deposition of Electroactive Polymers for Light-emitting

Diodes and Photovoltaics: DMR-0208786Mary Galvin, University of Delaware and Lewis Rothberg, University of

Rochester

EducationDuring the last year 1 student (Steve Konezny) and 1 Postdoctoral Fellow (Dr. Zhenjia Wang)received some financial support from this grant at the University of Rochester. Two students at

the University of Delaware were also at least partially supported on this grant (Yashpal

Bhandari and Changheui Ko). As part of their professional development all of the students

were encouraged to present their research at national meetings. Yashpal presented a poster at

the Spring MRS meeting. Steve presented his work at the APS meeting.

Changheui Ko and Galvin also used flexible PLEDS made in the Galvin lab as a demonstrationin an undergraduate engineering class, Introduction to Materials Science Class. The

demonstration was integrated into a section on semiconducting materials.

OutreachThis year Galvin was involved in teas and socials aimed at mentoring women graduate students

and faculty at the University of Delaware. Additionally she gave a presentation on the important

role mentors play in career development to a meeting of the Delaware Chapter of the Society ofWomen Engineers.

Figure 1: PLED made on a plastic

substrate used as a class

demonstration.