5 years ago

Orientation Control of Solution-Processed Organic Semiconductor Crystals To Improve Out-of-Plane Charge Mobility

Orientation Control of Solution-Processed Organic Semiconductor Crystals To Improve Out-of-Plane Charge Mobility
Xiaoshen Bai, Sangchul Lee, Alejandro Briseno, Jeremy S. Mehta, Jeffrey M. Mativetsky, Bart Kahr, Kaitlyn Molnar, Jack Ly, Megan Hand, Stephanie S. Lee, Kai Zong
The crystallization of a series of triisopropylsilylethynyl (TIPS)-derivatized acene-based organic semiconductors drop cast from solution onto substrates was investigated as a function of the size of their conjugated cores. When drop cast onto a substrate, the molecules in TIPS-pentacene crystals adopt a “horizontal” orientation, with the long axis of the pentacene core parallel to the substrate surface. For crystals comprising molecules with dibenzopyrene, anthanthrene, and pyranthrene cores, two-dimensional X-ray diffraction patterns revealed the existence of a second population of crystals adopting a “vertical” molecular orientation with the long axis of the acene core perpendicular to the substrate surface. The ratio of the population of TIPS-pyranthrene crystals with molecules adopting horizontal versus vertical orientations was controlled by varying the surface energy of the underlying substrate. These crystals displayed orientation-dependent linear birefringence and linear dichroism, as observed by differential polarizing optical microscopy. Conductive atomic force microscopy (C-AFM) revealed a 42-fold improvement in out-of-plane hole mobility through crystals adopting the vertical molecular orientation compared to those adopting the horizontal molecular orientation.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b02771

DOI: 10.1021/acs.chemmater.7b02771

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