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Thermoelectric devices are an emerging green technology that turn heat into electricity or vice versa without any moving parts. They have not yet seen wide-spread use outside of niche applications because thermoelectric materials are either too costly or too inefficient. Copper Selenide (Cu2Se) has one of the highest thermoelectric efficiencies of any bulk material and it can be synthesized inexpensively via solution-deposition. We characterize thin-films of solution-deposited Cu2Se nanoparticles annealed at different temperatures. The direct current (DC) and terahertz (THz) conductivities of samples annealed at 200 °C or above are two orders of magnitude greater than that of the 100 °C and unannealed sample. We find the THz conductivity of samples annealed at 300 °C or greater to be frequency-independent, thus their electrical properties are closer to that of a polycrystalline thin metal film than a nanomaterial. We measure DC and THz conductivity as a function of temperature and observe a feature at 350 K attributable to Cu2Se's second-order phase transition to super-ionic conductivity. This is 60 K cooler than the transition temperature in bulk Cu2Se. Both DC and THz conductivity exhibit hysteresis over temperature cycling when heated past the phase transition.
Lupu-Gladstein, Noah B., "Electrical and Morphological Characterization of Annealed Solution-deposited Cu2Se Nanoparticle Thin-films" (2016). Physics and Astronomy Honors Projects. Paper 21.
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