Thermoelectric properties of large-scale Zn3P2 nanowire assemblies

Gram quantities of both unfunctionalized and 1,4-benzenedithiol (BDT) functionalized zinc phosphide (Zn3P2) nanowire powders, synthesized using direct reaction of zinc and phosphorus, were hot-pressed into highly dense pellets (≥98% of the theoretical density) for the determination of their thermoelectric performance. It was deduced that mechanical flexibility of the nanowires is essential for consolidating them in randomly oriented fashion into dense pellets, without making any major changes to their morphologies. Electrical and thermal transport measurements indicated that the enhanced thermoelectric performance expected of individual Zn3P2 nanowires is still retained within large-scale nanowire assemblies. A maximum reduction of 28% in the thermal conductivity of Zn3P2 resulted from nanostructuring. Use of nanowire morphology also led to enhanced electrical conductivity in Zn3P2. Interface engineering of the nanowires in the pellets, accomplished by hot-pressing BDT functionalized nanowires, resulted in an increase on both the Seebeck coefficient and the electrical conductivity of the nanowire pellets. It is believed that filtering of low energy carriers resulting from the variation of the chemical compositions at the nanowire interfaces is responsible for this phenomenon. Overall, this study indicated that mechanical properties of the nanowires along with the chemical compositions of their surfaces play a hitherto unknown, but vital, role in realizing highly efficient bulk thermoelectric modules based on nanowires.