Quantitative Nanoscale Mapping with Temperature Dependence of the Mechanical and Electrical Properties of Poly(3-hexylthiophene) by Conductive Atomic Force Microscopy

Using conductive atomic force microscopy, we introduce a method to simultaneously acquire electrical space-charge-limited current current measurements and material properties such as Young's modulus and surface adhesion with nanoscale resolution. We demonstrate the utility of this method using thin films of the prototypical, semiconducting polymer poly(3-hexylthiophene) (P3HT). Arrays of force-distance and current-voltage curves are acquired simultaneously, allowing the investigation of spatial heterogeneity and statistical analysis of correlations between material properties. Tip-surface contact mechanics are used to calculate the contact areas, allowing the accurate quantification Of charge transport properties through the fitting of space-charge-limited current to a modified Mott-Gurney model to extract the charge transport mobility accurately at each point. Measurements were taken from room temperature to 140 degrees C under a constant nitrogen flow to investigate changes in the properties of P3HT under standard annealing conditions. The quantitative analysis of temperature-dependent charge transport and mechanical properties of P3HT is consistent with grain boundary limited transport models and shows qualitatively different behavior for annealed and unannealed samples. The acquisition and analysis procedures developed here are generally applicable to the study of a wide range of organic semiconductor thin films.