Nano-films of carbo-benzene derivatives: Scanning probe microscopy analysis and prospects of use in organic solar cells

Abstract Three carbo-mer derivatives based on a C18Ph4 core decorated with two identical electro-active groups X, i.e. two aromatic carbo-benzenes (1 and 2, X = 4-anilinyl) and one pro-aromatic carbo-quinoid (the carbo-TTF 3, X = 1,3-dithiol-2-ylidene) were studied through Scanning Probe Microscopies (SPMs). Self-Assembled Monolayers (SAMs) were fabricated (thickness ~160 pm), for the two centrosymmetric representatives 1 and 3, the organization of which on the HOPG substrate was found to be structure-specific. Electrical/electronic properties of the three carbo-mers were determined by using Atomic Force Microscopy (AFM) and its electrical modes: Kelvin Probe Force Microscopy (KPFM) and conductive Atomic Force Microscopy (c-AFM). Measurements of the work function (∅) through KPFM result in a ∅ = 5.60 eV value for 1, 4.97 eV for 2 and 4.82 eV for 3. Hole mobility (µ) values extracted from local I-V plots by using c-AFM are 15 × 10 − 8 cm 2 V − 1 s − 1 for 1, 3 × 10 − 6 cm 2 V − 1 s − 1 for 2 and 87 × 10 − 8 cm 2 V − 1 s − 1 for 3. A concept test of the possible application of carbo-mers in self-assembled hole transporting monolayer (SA-HTM), with the view to replacing the most common p-type contact used in organic solar cells (OSCs), PEDOT:PSS, is also reported.