Charge Carrier Traps in Organic Semiconductors and Their Impact on Device Performance

Abstract: Organic semiconductors provide an opportunity to augment Silicon electronics in non-traditional areas such as clothing, flexible, rollable, and bio-integrated devices. Emerging exciting applications are near validation, hindered only by insufficient performance. Organic semiconductors are highly susceptible to defect formation, owing to their weak intermolecular interactions, and the electronic states formed in the gap typically reduce device performance. In this talk, I will discuss the origin and energetic distribution of several different types of traps in organic semiconductors and their impact on device performance. First, I will discuss the case of isomer coexistence, and provide evidence that when one isomer creates a discrete trapping state in the band structure of the other, the device performance is significantly reduced. Next, the influence of the polaronic effects and thermally generated microstrain at device interfaces will be described. The consecutive layers often have very different mechanical and thermal properties, therefore exhibiting different responses to external stimuli. These effects are widely overlooked in spite of their ubiquitous presence in layered devices. I will show that the inhomogeneous strain induced in organic semiconductor layers by virtue of the mismatch in the coefficients of thermal expansion of the consecutive layers increases the interfacial electronic trap density, lowers the mobility, and can induce a crossover from band-like to activated transport. Since the uncontrollable nature of the film formation overwhelms the fabrication benefits of solution deposition, in the last part of the talk I will introduce laser-printing, a solvent-free additive manufacturing method that allowed for simultaneous deposition and patterning of organic transistors on flexible substrates.

Bio: Oana Jurchescu is an Associate Professor of Physics at Wake Forest University (WFU). She received her PhD in 2006 from University of Groningen, the Netherlands, and was a postdoctoral researcher at the National Institute of Standards and Technology in Gaithersburg, MD, until 2009, when she joined the Physics Department at Wake Forest University as an Assistant professor. Her expertise is in charge transport in organic and organic/inorganic hybrid semiconductors, device physics and semiconductor processing. She published 80 peer-reviewed articles, 4 invited book chapters, 3 patents and gave over 50 invited or plenary talks at conferences. She won the 2013 National Science Foundation CAREER award, the ORAU Ralph E. Powe Junior Faculty Enhancement award, the WFU award for excellence in research, the WFU innovation award, the WFU prize for excellence in teaching and the WFU award for excellence in mentoring. She is associate editor for Journal of Materials Chemistry C and a member of the editorial board from Scientific Reports (Nature publishing group). She served in a variety of capacities, including program chair and co-chair, for over 30 international conferences and workshops such as MRS, APS, SPIE, etc.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.