Germanium (Ge) is an extensively studied element and widely used in the semiconductor industry. However, its use as a charge-generating medium in photovoltaics is limited by its inefficient light absorption due to the indirect band gap. It has been proposed that the indirect band gap of germanium can be switched to become direct after alloying with tin thereby rendering the material a better light absorber. However, the large lattice strain and low solubility of tin in germanium makes it challenging to obtain such alloys in bulk. Nonetheless, utilizing the nanocrystals’ ability to relax large lattice strain combined with a particular selection of precursor molecules, we have already achieved1 the synthesis of SnxGe1-x alloy nanocrystals with x up to 0.4. Here we report further improvements in the synthesis of SnxGe1-x nanoalloys that yielded the product with tin content up to 95% pushing the composition limit. X-ray diffraction, TEM and EDX mapping analysis have confirmed the presence of homogenous alloys over the full composition range. Mechanistic and computational studies of the material formation point to the reaction pathway through the formation of intermediate cubane-like Sn-Ge imide clusters. Absorption spectroscopy of NCs of varying composition demonstrates a pronounced red-shift and increase in molar absorptivity as a more direct indicator of changes in the electronic structure toward direct band gap behavior with increasing Sn-content. The details of the synthetic approach together with results of the structural, optical characterizations and mechanistic investigation will be presented. Mechanistic implications of Sn-Ge nanoalloy formation allowed us to introduce silicon into the alloy composition and the preliminary results on the synthesis of SixGeySn1-x-y nanoalloys will also be discussed. References: 1. Ramasamy, K.; Kotula, P. G.; Fidler, A. F.; Brumbach, M. T.; Pietryga, J. M.; Ivanov, S. A. Chem Mater. 2015, 27, 4640-4649.

Cubic SnxGe1-x nanoalloys: Beyond bulk composition limit

251st National Meeting (2016)

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