Structural stability of naphthyl end-capped oligothiophenes in organic field-effect transistors measured by grazing-incidence X-ray diffraction in operando

We report on microstructural durability of 5,5'-bis(naphth-2-yl)-2,2'-bithiophene (NaT2) in organic field-effect transistors (OFETs) in operando monitored by grazing-incidence X-ray diffraction (GIXRD). NaT2 maintains its monoclinic bulk motif in operating OFETs with a = 20.31 +/- 0.06 angstrom, b = 6.00 +/- 0.01 angstrom, c = 8.17 +/- 0.04 angstrom and beta = 96.64 +/- 0.74 degrees. Crystallites appear as a mosaic of single crystals reaching through the whole 50 nm thick active layer. The lattice parameters variation (<1%) falls within the statistical error of structure refinement when the OFET gate voltage is varied from 0 V to -40 V; or when the OFET is continuously cycled within this voltage interval over more than 10 h period. Within the first few cycles, both the hole mobility and threshold voltage are changing but then reach stable levels with an average mobility of (3.25 +/- 0.04) x 10(4) cm(2)/Vs and an average threshold voltage of -13.6 +/- 0.2 V, both varying less than 4% for the remainder of the 10 h period. This demonstrates crystalline stability of NaT2 in operating OFETs. (C) 2017 Elsevier B.V. All rights reserved.