Tracing Electrons in Organic Optoelectronic Materials

Abstract: Organic semiconductors are appealing for optoelectronic devices like solar cells and lighting and displays due to their low fabrication cost and energy input, tunable band gaps, and mechanical characteristics like their light weight and flexibility. However, these materials made of light atoms have low dielectric constants and small spin-orbit coupling to promote (reverse) intersystem crossing, as well as strong vibrational coupling leading to excitations and charges that are strongly influenced by the local environment and details of electron-hole wavefunctions. Approaches to these challenges involve engineering electronic energy levels and frontier molecular orbitals in a way that promotes energy flow that is favourable for devices.

I will describe our work on these problems coming from the molecular-scale perspective of scanning tunnelling microscopy and spectroscopy (STM/STS) to investigate energy level alignment at interfaces^1,2 and investigation of the frontier molecular orbitals of acceptor-donor complexes³. We have found, perhaps unsurprisingly, that the local environment can play a substantial role in determining energy levels and optoelectronic properties. While STM and STS give us an exquisite local view of these systems however, it is the dynamics that ultimately dictate device function. Here instead, we turn to time-resolved angle-resolved photoemission spectroscopy to probe the fate of excitations, and I will show some of our first results on neat C60 films.

1. Cochrane, K.A., Schiffrin, A., Roussy, T.S., Capsoni, M. & Burke, S.A. Nat. Commun. 6, 8312 (2015).
2. Cochrane, K.A. et al. J. Phys. Chem. C 122, 8437–8444 (2018).
3. Mayder, D.M. et al. Chem. Mater. 34, 2624–2635 (2022).
    

Bio: Dr. Sarah Burke is an Associate Professor in the departments of Physics & Astronomy, and Chemistry, and a Principal Investigator in the Stewart Blusson Quantum Matter Institute at the University of British Columbia. Her research uses scanning probe microscopy techniques to investigate materials from the atomic scale up.  Burke received her Bachelor’s Degree from Dalhousie University in 2002 (Honours in Physics) and her Master’s and Doctoral Degrees in Physics from McGill University in 2004 and 2009 respectively, where she focused on studying the growth and epitaxy of organic molecules on insulating surfaces using non-contact atomic force microscopy.  She then held an NSERC Postdoctoral Fellowship at UC Berkeley with Michael Crommie where she investigated graphene nano-structures using low temperature scanning tunnelling microscopy and spectroscopy. 

Since arriving at the University of British Columbia in 2010 she has built an interdisciplinary research group approaching materials questions from the atomic scale, applying these techniques to a wide range of materials from superconductors to molecular materials for future devices and controlling surface reactivity.  She held the Canada Research Chair (Tier 2) in Nanoscience 2010-2020, received a Peter Wall Early Career Scholar Award for Interdisciplinary study 2011-2012, and the Killam Award for Excellence in Mentoring in 2022. 

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.