Controlled morphology of self-assembled microstructures via solvent-vapor annealing temperature and ambipolar OFET performance based on a tris(phthalocyaninato) europium derivative

Abstract

A novel homoleptic sandwich-type tris[2,3,9,10,16,17,23,24-octa(naphthoxy)phthalocyaninato] europium triple-decker complex Eu2[Pc(ONh)8]3 (1), having a low-lying LUMO energy level of – 4.0 eV and relatively narrow HOMO–LUMO separation of 1.13 eV, was designed and successfully synthesized. The OFET devices fabricated from this compound using a solution-based quasi-Langmuir-Shäfer (QLS) method display air-stable ambipolar performance with the carrier mobilities of (2.5 ± 0.5) × 10−6 cm2 V−1 s−1 for holes and (2.3 ± 0.3) × 10−6 cm2 V−1 s−1 for electrons, indicating its ambipolar semiconducting nature. Upon the o-dichlorobenzene (DCB) solvent vapor annealing at the temperature of 60, 80, 100, and 120 °C, a fine combination of the “oriented attachment” with Ostwald ripening process under controlled SVA environments leads to the growth of the first two-dimensional (2D) micro-sheet microstructures with tunable morphology including the fragment-like irregular polygons, quasi-four-corner sheets, squares, and clovers, respectively, from the nanoparticles of the pristine QLS film. This in turn results in the tunable OFET device performance with the carrier mobilities changing as a result of the morphologies and crystallinities. The best result was achieved for the most crystalline 2D squares-based devices with the carrier mobilities of 0.11 ± 0.03 cm2 V−1 s−1 for holes and 0.06 ± 0.02 cm2 V−1 s−1 for electrons.