title: Spectroscopy of discrete vertically oriented single-crystals of n-type tetraazaterrylene: understanding the role of defects in molecular semiconductor photovoltaics.
abstract: Recent synthetic work has realized a novel (n-type) small-molecule acceptor, 7,8,15,16-tetra-aza-terrylene (TAT), single-crystals of which can be grown oriented along the c-axis crystallographic direction, and over-coated with pentacene to form a highly ordered donor/acceptor interface for use in organic photovoltaic devices. However, characterization of single TAT crystals reveals highly variable emission spectra and excited state dynamics - properties which strongly influence photovoltaic performance. Through the use of single-crystal widefield imaging, photoluminescence spectroscopy, time correlated single photon counting, and resonant Raman studies, we conclude that this variability is a result of long-lived low-energy trap-emission from packing defects. Interestingly, we also discovered that TAT crystals whose width exceeds ∼200 nm begin acting as waveguides and optical microcavity resonators for their own photoluminescence. Several strategies are proposed for leveraging the size-dependant optical properties of TAT pillars to further enhance device performance using this active layer design.
authors.affiliation: Department of Chemistry, University of Massachusetts, Amherst, MA, USA. mdbarnes@chem.umass.edu.
authors.forename: A J
authors.initials: AJ
authors.lastname: Wise
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: J
authors.initials: J
authors.lastname: Fan
authors.forename: F
authors.initials: F
authors.lastname: Wudl
authors.forename: A L
authors.initials: AL
authors.lastname: Briseno
authors.forename: M D
authors.initials: MD
authors.lastname: Barnes
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D055668:Photochemical Processes; D012666:Semiconductors; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D001372:Aza Compounds