Precision Doping of Iodine for Highly Conductive Copper(I) Iodide Suitable for the Spray-Printable Thermoelectric Power Generators
Eun Jin Bae, Jungwon Kim, Mijeong Han, Young Hun Kang
Abstract
A highly conductive copper iodide (CuI) film with excellent thermoelectric (TE) performance was simply prepared by using the solution-processable spray printing technique for the fabrication of transparent and flexible TE generators (TEGs). Compensating for sublimation- or evaporation-induced iodine loss during the spray printing process, the addition of a small amount (1 at. %) of iodine (I 2 ) into the CuI precursor solution was dramatically effective for obtaining CuI films showing the excellent electrical conductivity of 207.6 S·cm –1 and power factor of 673.3 μW·m –1 ·K –2, resulting in a high zT value of 0.31. Importantly, added I 2 played a critical role in increasing the electrical conductivity by providing iodide to improve the Cu to I stoichiometry in the CuI films and improve crystallite growth. Using 1 at. % I 2 doping, two different flexible TEGs (one coiled and one foldable) were successfully fabricated that showed a high output power density of 236.5 μW·cm –2 at a temperature gradient of 22 °C and high sensitivity to small temperature changes induced by a halogen lamp, respectively. This efficient and facile approach to fabricating solution-processable transparent conductors with high TE performance suggests potential applicability to the development of energy-harvesting windows or screens.