Direct mask-free patterning of molecular organic semiconductors using organic vapor jet printing

We demonstrate the solvent-free, high-resolution direct printing of molecular organic semiconductors for use in low cost optoelectronic applications. In this method, called organic vapor jet printing, hot inert carrier gas picks up the molecular organic vapor and expands it through a microscopic nozzle, resulting in physisorption of the molecules onto a cooled substrate. Pattern resolution and printing speed are determined by the nozzle shape, nozzle-to-substrate distance, downstream pressure, and molecular mass of the carrier gas. Quantitative models are developed using a combination of scaling analysis, direct simulation Monte Carlo modeling, and printing experiments. Pattern resolutions of up to $1000\mathrm{dpi}$ and local deposition rates exceeding $2300\mathrm{\AA }∕\mathrm{s}$ are achieved. Pentacene channel thin film transistors are printed at a local deposition rate of $700\mathrm{\AA }∕\mathrm{s}$ at both low and atmospheric pressures, resulting in a field-effect mobility of $0.25{\mathrm{cm}}^2∕\mathrm{Vs}$ and a current on/off ratio of $7\times {10}^5$ for devices grown at a background pressure of $0.24\mathrm{Torr}$ . The high directionality of the molecular jets and well-defined shape of the deposits enables combinatorial printing of structures and devices, while affording considerable control over film morphology. The method is also readily applicable to document printing using solvent-free inks.