Prof. Javier Vela, from Iowa State University, will present this seminar.
Phosphides. A critical aspect of the synthesis and application of nanostructured transition metal phosphides is to control their exact phase and stoichiometry, as these play key roles in determining their optoelectronic and catalytic properties. As a step in this direction, we have studied how the chemical structure and reactivity of a family of commercially available organo phosphite precursors (P(OR)3, R = alkyl or aryl) affect the evolution of nickel and nickel phosphide nanocrystals. Using a combination of experimental and computational methods, we show that different phosphite precursors selectively yield Ni, Ni12P5, and Ni2P phases, and that these evolve over time through multiple mechanistic pathways. We expect these results will help alleviate the need for more time-consuming testing and optimization of several different reaction conditions or unrelated precursors at random, thus enabling a faster development of these and similar nanostructured materials for practical applications.
Perovskites. Organolead halide perovskites are promising semiconducting materials for photovoltaic applications due to their high power conversion efficiency, tunable band gap, and low cost. Using a combination of structural and spectroscopic characterization methods, including powder X-ray diffraction, thermal analysis, and 207Pb solid-state NMR spectroscopy, we address some of the main challenges and possible solutions currently facing the field of organometal halide semiconductors. Thermal analysis reveals composition-dependent, divergent decomposition pathways in these materials. 207Pb ssNMR is particularly ideal for studying their local lead coordination environment, and reveals the formation of previously unsuspected amorphous phases and dopant impurities in these materials. We expect our results will help guiding the development of more thermally-, moisture-, and photo-stable perovskites and their solar cell devices.
