New pentacene crystalline phase induced by nanoimprinted polyimide gratings

Control of the polymorphism of organic semiconductor films is very important in optoelectronic devices, such as organic thin-film transistors, solar cells, and organic light-emitting diodes. Here, we show the use of polyimide nanogratings (PI-NGs) patterned by nanoimprint lithography to control the polymorphism of deposited pentacene films. Interestingly, a new crystalline phase is first found in the pentacene thin-film formed on the PI-NGs. This new phase, with a d-spacing of 1.35 nm, is more stable than the bulk and thin-film phases in the pentacene film, discussed in terms of X-ray diffraction (XRD) measurements and quantum theory calculations. The response mechanism of the formation of this new phase is characterized by XRD and atomic force microscopy; the polymorphism and surface morphology show a strong dependence on the width of PI-NGs. The size-dependent PI-NG responses of the pentacene film can also control the phase transition from the thin-film to the bulk phase.