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Posted: Jun 29, 2016
New approach to room-temperature materials synthesis: Low cost, simple, and controlled composition
(Nanowerk News) Templates are being exploited to create new materials for solar cells and other energy-producing devices. Now, a versatile two-step process uses templates of hexagonal nanoplates that controllably transform into more complex materials with specific sizes and shapes. Chemical processes known as ion exchange reactions convert templates of compounds containing two elements to new materials with three elements. The resulting material has controlled size, shape, and composition (Nanoscale, "Rapid direct conversion of Cu2-xSe to CuAgSe nanoplatelets via ions exchange reactions at room temperature").
A versatile two-step process allows for the controlled synthesis of new materials for energy technology. Hexagonal nanoplate templates undergo chemical reactions, while maintaining their shape and incorporating a new element. On the left is an electron image showing the surface of a hexagonal nanoplate. On the right are the elemental maps of the remainingcopper (red) and selenium (blue) from the template and the incorporated silver (purple). These maps were obtained with energy-dispersive X-ray spectroscopy. The copper selenide nanoplates transformed to a new material that contained silver.
This simple approach allows for earth-abundant energy materials to be made with a great degree of control over their chemical composition and shape, at low cost. Scientists used this approach for direct conversion, at room temperature, of copper selenide to a new material, copper silver selenide. This new material is a semiconductor useful for solar cells and converting waste heat to electricity.
Researchers at the University of Michigan discovered a method for direct conversion, at room temperature, of copper selenide to copper silver selenide, which is a valuable semiconductor. The chemical composition of the reaction product is controlled by adjusting the silver to selenium (Ag:Se) molar ratio in the starting reactants. The shape is controlled by tuning the reaction temperature and time during formation of copper selenide crystals.
The approach involves chemical processes called ion exchange reactions. In the ion exchange reactions, the partial removal of smaller copper ions from copper selenide crystals occurs. Immediately, the same amount of slightly larger silver ions replace these lost copper ions, while preserving the shape of the original crystals.
This simple two-step batch process represents an energy-efficient, cost-efficient, and versatile strategy to create materials with lower defect density and superior performance. The resulting new semiconductor could be used for advanced solar cells and thermoelectrics.