Nanoimaging of Orientational Defects in Semiconducting Organic Films

N. Mrkyvkova, A. Cernescu, Z. Futera, A. Nebojsa, A. Dubroka, M. Sojkova, M. Hulman, E. Majkova, M. Jergel, P. Siffalovic and F. Schreiber

J. Phys. Chem. C 125, 9229 (2021)
The development of defect analysis for inorganic semiconductors in the past century paved the way for the success story of today’s electronics. By analogy, defect analysis plays a critical role in developing and improving devices based on organic molecular semiconductors. However, because of weak molecular interactions, absent in inorganic semiconductors, device-relevant thin organic films are susceptible to the formation of defects in the molecular orientation, which in turn have a profound impact on the performance in the optoelectronic applications. To address this problem, we broaden the applicability of scattering-type scanning near-field optical microscopy (s-SNOM) and utilize the light-induced anisotropic response of vibrational modes to reveal the defects in molecular orientation. We show that in the case of molecular islands with steep crystal facets only the scattered s-SNOM optical amplitude can be exploited to describe the molecular arrangement reliably, while the phase-based analysis leads to artifacts. The presented s-SNOM analysis of molecular defects can be universally applied to diverse topographies, even at the nanoscale.