Asymmetric Surface Potential Energy Distributions in Organic Electronic Materials via KPFM

Paula B. Hoffmann, Adam G. Gagorik, Xialing Chen, and Geoffrey R. Hutchison. “Asymmetric Surface Potential Energy Distributions in Organic Electronic Materials via KPFM” J. Phys. Chem. C, 2013, 117 (36), pp 18367–18374. Online. Supporting Information is available here: HoffmannSI

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.