Organic single-crystalline p-n junctions are grown from mixed solutions. First, C60 crystals (n-type) form and, subsequently, C8-BTBT crystals (p-type) nucleate heterogeneously on the C60 crystals. Both crystals continue to grow simultaneously into single-crystalline p-n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single-crystalline p-n junctions.

Conjugated polymers are the primary blocks for organic electronics. Traditionally, conjugated polymers synthesized via Suzuki, Heck, and Stille couplings are catalyzed by soluble homogeneous ligated palladiums, which suffer the contaminations of residual nano-palladium and phosphine impurity resulting from side reaction of aryl−aryl exchange. To overcome these drawbacks, a commercially available, clean, and ligand-free heterogeneous catalyst Pd/C for the C−C coupling polymerizations was developed in this work. The Pd/ C catalyst showed increases in catalytic activity for Suzuki and Heck polymerizations, as compared with the classical homogeneous catalyst Pd(PPh 3 ) 4 . Furthermore, the Pd/C catalyst exhibited advantage of much less Pd residue in the resulting polymers, leading to better charge transport properties as demonstrated by field effect transistors.

Metal oxide resistive memory devices based on Ta 2 O 5 have demonstrated high switching speed, long endurance, and low set voltage. However, the physical origin of this improved performance is still unclear. Ta 2 O 5 is an important archetype of a class of materials that possess an adaptive crystal structure that can respond easily to the presence of defects. Using first principles nudged elastic band calculations, we show that this adaptive crystal structure leads to low energy barriers for inplane diffusion of oxygen vacancies in k phase Ta 2 O 5. Identified diffusion paths are associated with collective motion of neighboring atoms. The overall vacancy diffusion is anisotropic with higher diffusion barriers found for oxygen vacancy movement between Ta-O planes. Coupled with the fact that oxygen vacancy formation energy in Ta 2 O 5 is relatively small, our calculated low diffusion barriers can help explain the low set voltage in Ta 2 O 5 based resistive memory devices. Our work shows that other oxides with adaptive crystal structures could serve as potential candidates for resistive random access memory devices. We also discuss some general characteristics for ideal resistive RAM oxides that could be used in future computational material searches.

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