A Molecular Precursor Solid-State Route to Inorganic Nanoparticles
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Iron Pyrite (FeS2) has been the center of development to obtain a high efficiency, low-cost, earth-abundant and environmental-friendly photovoltaic absorber materials in the field of solar research for many decades. Many studies have offered explanations attempting to solve the conundrum, but, between the innate and unsolvable stoichiometric and phase instability challenges and the contradictory conclusions, no effective solution has been made to address pyrite’s failing to reach its theoretical capability.
Iron germanium sulfide (Fe2GeS4) has recently emerged as a potential thin-film photovoltaic absorber material to replace its binary predecessor. With the introduction of the third element, germanium (Ge), the new ternary material was theorized to confer better thermal stability while improving with better band-gap and retaining the favorable low-cost of production traits enjoyed by iron pyrite. This work proposes a facile solid-state synthesis route to obtain high-quality, phase pure Fe2GeS4 nanoparticles from molecular precursors undergoing mechanical mixing and a two-hour annealing procedure under a sulfur-rich atmosphere. Analysis of the resulting Fe2GeS4 product has demonstrated good thermal stability under elevated temperatures (up to 500 ˚C), and the elimination of the phase coexistence challenge in comparison to pyrite. A comprehensive phase shift mechanism of iron chalcogenides and a Fe2GeS4 reaction mechanism is proposed to supplement the discussion of pyrite’s phase instability. A facile thin-films fabrication is designed by undergoing further mechanical processing and annealing treatment and is revealed that Fe2GeS4 withstands high temperature in the thin-film device.