Oligothiophene Derivatives Functionalized with a Diketopyrrolopyrrolo Core for Solution-Processed Field Effect Transistors: Effect of Alkyl Substituents and Thermal Annealing

Two new oligothiophene derivatives bearing a diketopyrrolopyrrole core, 2,5-di-n-hexyl-3,6-bis(5′′-n-hexyl[2,2′;5′,2′′]terthiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (DHT6DPPC6) and 2,5-di-n-dodecyl-3,6-bis(5′′-n-hexyl[2,2′;5′,2′′]terthiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (DHT6DPPC12), and their use in solution-processed organic field effect transistors are reported. Depending on the type of alkyl substituent and film annealing temperature, the crystal grain sizes and interlayer spacing vary as observed using atomic force microscopy and X-ray diffractometry, respectively. These changes in film morphology and interlayer spacing lead to an order of magnitude difference in the field effect mobilities. The field effect mobilities for annealed DHT6DPPC6 and DHT6DPPC12 films are 0.02 and 0.01 cm2/V s, respectively.