Charge carrier transport in organic electronic devices is influenced by the crystalline microstructure and morphology of the organic semiconductor film. Evaporation behavior during drying plays a vital role in controlling the film morphology and the distribution of solute in inkjet-printed films. On p. 229, Kilwon Cho and co-workers demonstrate the influence of the evaporation-induced flow in a single droplet on the crystalline microstructure and film morphology of inkjet-printed 6,13-bis((triisopropylsilylethynyl) pentacene. The results provide an excellent method for direct-write fabrication of high-performance organic electronics.
We have demonstrated the influence of evaporation-induced flow in a single droplet on the crystalline microstructure and film morphology of an ink-jet-printed organic semiconductor, 6,13-bis((triisopropylsilylethynyl) pentacene (TIPS_PEN), by varying the composition of the solvent mixture. The ringlike deposits induced by outward convective flow in the droplets have a randomly oriented crystalline structure. The addition of dichlorobenzene as an evaporation control agent results in a homogeneous film morphology due to slow evaporation, but the molecular orientation of the film is undesirable in that it is similar to that of the ring-deposited films. However, self-aligned TIPS_PEN crystals with highly ordered crystalline structures were successfully produced when dodecane was added. Dodecane has a high boiling point and a low surface tension, and its addition to the solvent results in a recirculation flow in the droplets that is induced by a Marangoni flow (surface-tension-driven flow), which arises during the drying processes in the direction opposite to the convective flow. The field-effect transistors fabricated with these self-aligned crystals via ink-jet printing exhibit significantly improved performance with an average effective field-effect mobility of 0.12 cm2 V–1 s–1. These results demonstrate that with the choice of appropriate solvent ink-jet printing is an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct-write fabrication of high-performance organic electronics.