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A key challenge of discovering and engineering novel organic-film devices is understanding how the complex interplay between crystalline structure, orientation, and molecular packing determines the electronic properties of these thin films. In a new article published in Advanced Functional Materials (http://dx.doi.org/10.1002/adfm.201502412), Princeton Ph.D. candidate Geoff Purdum in Lynn Loo’s group in the Chemical and Biological Engineering Department at Princeton and his co-authors shed new light on this issue. In particular, they report reversible access of two polymorphs exhibited by core-chlorinated naphthalene tetracarboxylic diimide (NTCDI-1), an organic semiconductor developed by BASF. Detailed studies reveal that although the monoclinic polymorph of this compound exhibits superior electronic properties as a single crystal, nevertheless when produced as thin films, it is the triclinic phase that exhibits better charge transport properties. Careful structural studies, including in-situ GIWAXS performed at the G1 station at CHESS, suggest that in-plane charge transport anisotropy is more important than the polymorphic packing motif in this case, which may provide important guidance for future work in this ever-evolving field.
(a) Sequence of GIWAXS images, obtained at CHESS station G1 using an in-situ furnace, showing the monoclinic to triclinic phase transformation. (b) Integrated intensities of several Bragg Peaks from (a).
Submitted by: Arthur Woll, CHESS, Cornell University
10/07/2015