Researchers using the ChemMatCARS 15-ID-B,C,D beamline at the APS report the first trap-clearing spectra in electron-conducting organic semiconductors. This research could serve as a foundation for further microscopic studies of trap-formation and trap-clearing mechanisms.
Perylene diimide (PDI) derivatives are important components of organic circuits and photovoltaic systems, but the electron trapping mechanism(s) in higher-LUMO PDIs (−3 to −4 eV, where radical anions are expected to react with atmospheric water and oxygen) are not well characterized. Here, we examine the spatial distribution of traps in transistors made from PDIs with these higher LUMO levels, and measure trap-clearing spectra in n-type organic materials using time- and wavelength-resolved frequency-modulated Kelvin probe force microscopy (FM-KPFM). We find that the rate of trap-clearing under visible light does not follow a LUMO-level trend, and we observe spectral evidence for different trapping mechanisms on bare versus HMDS-treated SiO2.
Louisa M. Smieska, Zhong Li, David Ley, Adam B. Braunschweig and John A. Marohn, “Trap-clearing Spectroscopy in Perylene Diimide Derivatives,” Chemistry of Materials, Just Accepted Manuscript, DOI: 10.1021/acs.chemmater.5b04025, Published Online January 21, 2016.