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Concept
Zinc phosphide
Summary
Zinc phosphide (Zn3P2) is an inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black. It is used as a rodenticide. Zn3P2 is a II-V semiconductor with a direct band gap of 1.5 eV and may have applications in photovoltaic cells. A second compound exists in the zinc-phosphorus system, zinc diphosphide (ZnP2).
Zinc phosphide can be prepared by the reaction of zinc with phosphorus; however, for critical applications, additional processing to remove arsenic compounds may be needed.
6 Zn + P4 → 2 Zn3P2
Another method of preparation include reacting tri-n-octylphosphine with dimethylzinc.
Zinc phosphide reacts with water to produce phosphine (PH3) and zinc hydroxide (Zn(OH)2):
Zn3P2 + 6 H2O → 2 PH3 + 3 Zn(OH)2
Zn3P2 has a room-temperature tetragonal form that converts to a cubic form at around 845 °C. In the room-temperature form there are discrete P atoms, zinc atoms are tetrahedrally coordinated and phosphorus six coordinate, with zinc atoms at 6 of the vertices of a distorted cube.
The crystalline structure of zinc phosphide is very similar to that of cadmium arsenide (Cd3As2), zinc arsenide (Zn3As2) and cadmium phosphide (Cd3P2). These compounds of the Zn-Cd-P-As quaternary system exhibit full continuous solid-solution.
Zinc phosphide is an ideal candidate for thin film photovoltaic applications, for it has strong optical absorption and an almost ideal band gap (1.5eV). In addition to this, both zinc and phosphorus are found abundantly in the earth's crust, meaning that material extraction cost is low compared with that of other thin film photovoltaics. Both zinc and phosphorus are also nontoxic, which is not the case for other common commercial thin film photovoltaics, like cadmium telluride.
Researchers at the University of Alberta were the first to successfully synthesize colloidal zinc phosphide. Before this, researchers were able to create efficient solar cells from bulk zinc phosphide, but their fabrication required temperatures greater than 850 °C or complicated vacuum deposition methods.
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