(66d) Fabrication of Transition Metal Chalcogenide Cu2Se Semiconducting Thin Films and Thermoelectric Property Characterization

The global energy crisis and environmental problems caused by large-scale industrial development have drawn attention to alternative energy sources. Thermoelectric (TE) materials, which convert electricity to heat and vice versa, may offer solutions to these issues via waste heat recovery, power generation, and solid-state cooling. However, most TE materials are fabricated from toxic materials such as tellurium and lead. Hence, we plan on using solution processed flexible thin films of sustainable thermoelectric materials. Copper selenide (Cu2Se), a transition metal chalcogenide and p-type semiconductor, exhibits good thermoelectric performance in a wide temperature range and is more environmentally friendly compared to current toxic TE materials.

The goal of this work is to determine reliable, low-energy and low-cost routes of fabricating Cu2Se thin films with high figure of merit, ZT, which quantifies the thermoelectric performance of a material. To obtain a high ZT value, both Seebeck coefficient and electrical conductivity must be large and thermal conductivity should be minimized. This is fundamentally difficult to achieve because reduction in thermal conductivity is typically accompanied by a large penalty to electrical conductivity. Nanostructured materials and thin films can potentially break this relationship between the electronic and thermal properties of a material. We adopt two methods of making Cu2Se thin films: 1) Directly fabricate nanostructured Cu2Se thin films using a solvent deposition process and dope the films; 2) Using a cation exchange process using cadmium selenide nanocrystals. We perform structural characterization of our thin films via x-ray diffraction and scanning electron microscopy. Through electrical conductivity and Seebeck coefficient measurements, we compare their thermoelectric properties and optimize ZT values by varying their chemical composition and film morphology.