Thin film growth by high vacuum evaporation of the n-type organic semiconductor 5, 5'''-diperfluorohexylcarbonyl-2,2':5',2":5",2'''-quaterthiophene (DFHCO-4T) on poly-(α-methylstyrene)-coated n~(++)-Si/SiO_2 substrates is investigated at various deposition fluxes and substrate temperatures. Film characterization by atomic force microscopy reveals typical Stransky-Krastanov growth. Transistors with Au source-drain top contacts and optimized DFHCO-4T deposition conditions attain an apparent saturation mobility of 4.6cm~2/Vs, whereas this parameter is 100× lower for similar transistors with LiF/Al top contacts. We explain this lower performance by the formation of a thin interfacial layer with poor injection properties resulting from a redox reaction between Al and DFHCO-4T.
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