Growth dynamics of pentacene thin films

The recent demonstration of single-crystal organic optoelectronic devices h as received widespread attention(1-4). But practical applications of such d evices require the use of inexpensive organic films deposited on a wide var iety of substrates. Unfortunately, the physical properties of these organic thin films do not compare favourably to those of single-crystal materials. Moreover, the basic physical principles governing organic thin-film growth and crystallization are not well understood. Here we report an in situ stu dy of the evolution of pentacene thin films, utilizing the real-time imagin g capabilities of photoelectron emission microscopy. By a combination of ca reful substrate preparation and surface energy control, we succeed in growi ng thin films with single-crystal grain sizes approaching 0.1 millimetre (a factor of 20-100 larger than previously achieved), which are large enough to fully contain a complete device. We rnd that organic thin-film growth cl osely mimics epitaxial growth of inorganic materials, and we expect that st rategies and concepts developed for these inorganic systems will provide gu idance for the further development and optimization of molecular thin-film devices.