Solution-Processable α,ω-Distyryl Oligothiophene Semiconductors with Enhanced Environmental Stability

We describe the rational design of oligothiophene semiconductors to facilitate solution-based fabrication of environmentally stable organic field-effect transistors (OFETs). Ultrathin films of α,ω-distyryl quaterthiophene (DS4T), pentathiophene (DS5T), and sexithiophene (DS6T) were prepared via solution processing to probe the effect of styryl end groups, oligomer length, and thin film structure on air stability. These films were prepared via solution deposition and thermal annealing of precursors featuring thermally labile ester solubilizing groups. A detailed study of the thin film structure was performed using atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and grazing incidence X-ray diffraction (GIXD). Functional OFETs were obtained for DS5T and DS6T and have, respectively, hole mobilities of 0.051 and 0.043 cm2/(V s) and on/off ratios of 1 × 105 to 1 × 106, whereas DS4T OFETs failed to function because of poor film continuity. The effect of both short-term and long-term exposure to air is tracked in OFETs revealing remarkable stability for both DS5T and DS6T. This stability is attributed to the elimination of reactive sites in α,ω-distyryl oligothiophenes and suggests that careful choice of end-group structure can stabilize these molecules against oxidative degradation.