  Organic electronic materials have potential applications in a number of
low-cost, large area electronic devices such as flat panel displays and
inexpensive solar panels. Small molecules in the series Anthracene, Tetracene,
Pentacene, are model molecules for organic semiconductor thin films to be used
as the active layers in such devices. This has motivated a number of studies of
polyacene thin film growth and structure. Although the majority of these
studies rely on vapor-deposited films, solvent-based deposition of films with
improved properties onto non-crystalline substrates is desired for industrial
production of devices. Improved ordering in thin films will have a large impact
on their electronic properties, since grain boundaries and other defects are
detrimental to carrier mobilities and lifetimes. Thus, a long-standing
challenge in this field is to prepare largearea single crystal films on
arbitrary substrates. Here we demonstrate a solvent-based method to deposit
thin films of organic semiconductors, which is very general. Anthracene thin
films with single-crystal domain sizes exceeding 1x1 cm2 can be prepared on
various substrates by the technique. Films of
6,13-bis(triisopropylsilylethynyl)pentacene are also demonstrated to have grain
sizes larger than 2x2 mm2. In contrast, films produced by conventional means
such as vapor deposition or spin coating are polycrystalline with micron-scale
grain sizes. The general propensity of these small molecules towards
crystalline order in an optimized solvent deposition process shows that there
is great potential for thin films with improved properties. Films prepared by
these methods will also be useful in exploring the limits of performance in
organic thin film devices.
