Improved alignment and crystallinity of TIPS-Pentacene thin films by off-center spin coating

A comprehensive study for crystal alignment of TIPS-Pentacene by an off-center spin coating has been presented. In a normal center spin coating method, the centrifugal force on the grains is multidirectional which results into crystals aligning in multiple directions depending on the location on the sample. However in an off-center spin coating method where the samples are kept at a distance away from the center, a unidirectional centrifugal force in the direction of the sample causes all the grains to align nearly in the direction of this force. The spin speed was the paramount factor influencing the overall grain size, whereas the overall alignment depends on the off-center distance. All the films in these experiments were found to have very large crystal sizes, ranging up to 5 microns. In addition, films formed by off-center method were found to be more crystalline than the center spin coated film and show a metastable crystalline polymorph.