Morphology and molecular orientation of thin-film bis(triisopropylsilylethynyl) pentacene

As a modification to the insoluble and herringbone-structured pentacene, bis(triisopropylsilylethynyl) (TIPS) pentacene has two bulky side groups, leading to good solubility in common organic solvents and regular π-π stacking arrangements in the crystalline state. Solution processing of TIPS-pentacene thin films was investigated as a function of various process parameters in this work. Electron diffraction results suggested that TIPS-pentacene molecules tended to align with the acene unit edge on to the substrate, touching down with their bulky side groups. In a TIPS-pentacene polycrystalline film, the long axis of individual crystallite is [2 1 0], while the shorter axis is [1 2̄ 0]. High-resolution electron microscopy was used to study the local crystal structure and characteristic defects of TIPS-pentacene thin films. Due to the nonaromatic side groups, TIPS-pentacene was found to be significantly more sensitive to the electron beam (critical dose J_c = 0.05 C/cm² at 300 kV) than pentacene itself (J_c = 0.2 C/cm² at 100 kV).