Organic field effect transistors from ambient solution processed low molar mass semiconductor-insulator blends

The morphology and organic field effect transistor (OFET) properties of two component blends of semi-crystalline 6,13-bis(triisopropylsilylethinyl) pentacene (TIPS-pentacene) with selected amorphous and semi-crystalline side chain aromatic low permittivity insulating binders deposited at room temperature under vacuum from a good solvent are reported. When blended with an amorphous binder there is evidence from X-ray photoelectron spectroscopy (XPS) of a strong interaction between TIPS-pentacene and the binder in the solidified film giving rise to twisted TIPS-pentacene crystals containing dislocations. Due to this strong interaction we see no evidence of segregation of TIPS-pentacene towards the active interface and hence we observe a rapid fall off in saturated hole mobility at an active concentration less than 50 wt%. When blended with a crystalline binder there is no evidence from XPS of any interaction between TIPS-pentacene and the binder in the solidified film. We propose that when a semi-crystalline binder is used, which crystallizes more slowly from solution than TIPS-pentacene, we observe stratification of the active material to both interfaces and as a result retention of saturated hole mobility even down to 10 wt%. The potential applications of the approach are in the formulation of low-cost organic semiconductors whose solution and solid state properties can be fine-tuned by careful binder selection.