Clancy group helps explain mobility breakthrough in fabricating large-area organic electronics
Graduate student Kristina Lenn and Professor Paulette Clancy, in collaboration with experimental groups at Stanford (Zhenan Bao's group) and KAUST (Aram Amassian), as well as synchrotron experts at CHESS (Smilgies) and SLAC (Mannsfeld), have recently published a paper in Nature Communications that describes how processing conditions can control organic crystal polymorphism to improve charge transport through use of appropriately sized solvent molecules.
They studied a common solution-processable organic semiconductor molecule, TIPS-pentacene, that –when sheared in solution- adopts metastable polymorphs (crystal structures) that have better charge transport characteristics for improved electronic devices. This paper features a combination of high-speed polarized optical microscopy, in situ microbeam GIWAXS (grazing wide-angle X-ray scattering) and molecular simulation to uncover the mechanisms that lie behind the choice of polymorphs.
Lenn and Clancy’s molecular-scale simulation showed that the larger the molar volume of the solvent molecule, the greater its tendency to disrupt the emerging crystal structure and destabilize the configurational stability of the crystal’s unit cell. Since the polymorphs are closely spaced in energy, even small changes can favor the formation of other structures and result in different charge mobility. The paper can be found at Nature Communications 5, Article number: 3573 (2014). doi:10.1038/ncomms4573