Controlling Crystallite Orientation of Diketopyrrolopyrrole‐Based Small Molecules in Thin Films for Highly Reproducible Multilevel Memory Device: Role of Furan Substitution

For the organic memory device with vertically arranged electrodes, controlling the film‐packing to achieve highly oriented crystallite arrangement is critical but challenging for obtaining the satisfied performance. Here, the effect of backbone planarity on the crystallite orientation is studied. Two diketopyrrolopyrrole‐based small molecules (NI 2 PDPP and NI 2 FDPP) are synthesized with increasing planarity by furan substitution for phenyl rings. Upon thin‐film analysis by atomic force microscopy, X‐ray diffraction, and grazing‐incidence small‐angle X‐ray scattering, the orientations of these crystallites are demonstrated to be well controlled through tailoring molecular planarity. The highly planar NI 2 FDPP in film prefers out‐of‐plane crystallite orientation with respect to the substrate normal while the nonplanar NI 2 PDPP displays less ordered packing with a broad orientation distribution relative to the substrate. As a result, NI 2 FDPP‐based memory device exhibits superior multilevel performance. More importantly, the oriented crystallite arrangement favors uniformity in NI 2 FDPP thin film, thus, the device displays higher reproducibility of memory effects. This study provides an effective synthetic strategy for designing multilevel memory materials with favorable crystallite orientation.