Fig. 2

Morphology and structure of the 1-μm-thick pentacene films as a function of concentration. a SEM cross-sections with a 1-μm scale bar. The dilute samples form large platelets typical of p-terphenyl, whereas an increase in dopant concentration leads to fragmentation into smaller faceted grains. b Close-up of the (003) peak where (*) corresponds to the pentacene peak position and (†) p-terphenyl position. The inset shows the contact angle of p-terphenyl (left) and pentacene (right) on the substrate. c Variation in scattering angle and grain size (calculated from the Scherrer equation ³¹) with increasing pentacene concentration, indicating a linear shift to towards lower scattering angles (i.e. increased lattice spacing); 5 and 100% pentacene are close to instrument resolution and consequently have the largest error in grain size. All films are 1 μm except the 100% pentacene which is 100 nm—XRD intensity is normalised to the thickness. The error in crystallite size was estimated as the difference between the Lorentzian and Gaussian calculation of the Scherrer equation.⁴⁷ d Unit cell of the pentacene showing the parallel dimer (teal) and herringbone dimer (cyan)