Bending-stress-driven phase transitions in pentacene thin films for flexible organic field-effect transistors

The effects of bending strain on the structure and electrical characteristics of pentacene films in flexible devices were investigated. It was found that the volume fraction of bulk phase in the pentacene film increases from 10.7% to 27.7% under 1.1% of tensile strain but decreases to 3.5% under 1.0% of compressive strain. These bending-stress-driven phase transitions between the bulk phase and the thin-film phase in the pentacene film resulted in the changes in field-effect mobility, and were driven by the differences between the in-plane dimensions of the crystal unit cells of the two phases to reduce the external bending stress.