This seems pretty amazing- Mr.Kim and John Sarik used a 3d printer configured as a plotter to print their own transistors. They appear to have tried a number of know recipes for OFETs, including TIPS-Pentacene and P3HT as semiconducting materials. Their results section is unfortunately a little light, so hopefully they will expand on their process characteristics in the future. In the meantime, the files that they used for printing are all available.