Asymmetric Surface Potential Energy Distributions in Organic Electronic Materials via Kelvin Probe Force Microscopy

Organic electronic devices promise
cheaper solution processability
than their inorganic counterparts and allow for the vast tailorability
of synthetic chemistry to tune properties and efficiency. A critical
fundamental challenge is to understand the dynamics and mechanisms
of charge transport, particularly the role of defects and traps. We
use Kelvin probe force microscopy to compare potential energy distributions
of organic, semiconducting thin films to comparable histograms calculated
via our dynamic Monte Carlo simulation. A combination of theoretical
and experimental investigations indicates that the common assumption
of a Gaussian disorder model (GDM) is not always a good approximation
for these materials. Instead we find asymmetric distributions due
to nanoscale heterogeneity of charge and a resulting mix of Lorentzian
and Gaussian disorder fit through a Voigt profile. Determining a more
accurate model for disorder in these commonly used materials has the
potential to influence the future of organic electronics design.