Methods to Mitigate Dopant-Induced Disorder in Organic Electronic Materials

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

NONTECHNICAL SUMMARY Organic semiconductors are promising materials for low cost, flexible electronics. Their electrical conductivity can be increased by adding positive or negative charges, a process known as molecular doping. However, the attraction between the opposite charges in organic semiconductors is stronger than in conventional semiconductors such as silicon. This can limit charge transport and reduce device performance. The goal of this project is to identify the physical properties that can weaken the attraction between the opposite charges. The PIs will combine experiments with simulation to understand which experimental parameters impact charge transport. These studies are important steps for realizing efficient and low-cost organic electronics such as solar cells, light-emitting diodes, transistors, and sensors. This work will train students at the frontiers of interdisciplinary and convergent materials research that combines experiments with computation. K-12 and undergraduate students will be introduced to materials science and the PIs will create on-line educational modules to teach numerical simulation to students. TECHNICAL SUMMARY Doping is required to raise the conductivity of organic semiconductors. However, doping adversely impacts charge transport through Coulomb interactions between charge carriers and ionized dopants, which are poorly screened by the low dielectric constants of organic materials. The goal of this project is to determine the influence of properties such as dielectric screening, ion-macromolecular interaction, and dopant distribution on the dopant-induced energetic disorder in a wide range of conjugated polymers without the need for additional synthetic modification. These studies test the hypothesis that the dopant-induced energetic disorder can be reduced by decreasing the Coulomb interaction between the dopant and the polymer. The investigators will measure two complementary charge transport parameters, the Seebeck coefficient and electrical conductivity, over a broad range of carrier concentrations and develop phonon-assisted hopping model to generate maps of the electronic density of states. This combined experimental-computation approach allows the investigators to extract carrier mobility and correlate dopant-induced energetic disorder with charge transport. The investigators combine space-charge limited current and Mott-Schottky measurements data with conductivity to validate the calculated mobility. These studies represent a significant and transformative step forward in the physical explanation of charge transport in doped conjugated polymers and providing structural design criteria to improve their performance. The investigators are training and mentoring a diverse next generation of chemists and materials scientists, performing outreach activities to introduce materials science to students across levels, and disseminating the hopping transport simulation tool on-line. 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.