Polymorph Transformation of Pentacene Thin Films Associated with Crystal‐to‐Liquid Crystal Transitions of Buffer Layers

ABSTRACT

A buried liquid crystal (LC) buffer layer is examined as a thermally switchable interface for post‐deposition irreversible polymorph transformation in pentacene thin films. Variable‐temperature 2D grazing‐incidence X‐ray diffraction (2D‐GIXD) reveals that pentacene on bare SiO ₂ /Si remains predominantly in the thin‐film phase after thermal cycling, whereas pentacene on Ph‐BTBT‐C10 undergoes an irreversible transformation from the thin‐film phase to the Campbell phase, coupled with the onset of the buffer crystal‐to‐LC transition. The extent of transformation is found to depend on the interfacial configuration of the pentacene/Ph‐BTBT‐C10 bilayer, i.e., whether Ph‐BTBT‐C10 is used as the underlayer or overlayer. Separate measurements on additional LC buffer layers reveal a certain association between pentacene transformation and buffer layer LC transition, indicating that buried LC interfaces may provide a means of facilitating post‐deposition polymorph conversion in organic semiconductor thin films.