Fig. 4
From: Crystal step edges can trap electrons on the surfaces of n-type organic semiconductors
Surface potential maps of crystal step edges and their role as electron traps. a–c SKPM surface potential images of Cl2-NDI single crystals with different thicknesses. Inset to a: schematic diagram of the SKPM measurement. Surface potentials averaging +60 mV were observed at discrete step edges in b. Inset to b: corresponding surface potential profile along the gray dashed line. The thicknesses of crystals were 2.7, 4.3, and 33.1 µm for a, b, c, respectively. d The proposed energy level diagram for step edges on the surface of Cl2-NDI single crystals. EF is the Fermi level and Evac is vacuum level. The work function of Cl2-NDI single crystal is ~5.2 eV. At the step edge, the vacuum level shifts about 0.06–0.18 eV compared to the surrounding surface by SKPM measurement. e The threshold voltage as a function of crystal thickness at VD of 10 V (74 devices) and 1 V (25 devices), respectively. The increase in VT with crystal thickness is indicative of increased electron trapping
