Precision Doping of Iodine for Highly Conductive Copper(I) Iodide Suitable for the Spray-Printable Thermoelectric Power Generators

Abstract

A highlyconductive copper iodide (CuI) film with excellent thermoelectric(TE) performance was simply prepared by using the solution-processablespray printing technique for the fabrication of transparent and flexibleTE generators (TEGs). Compensating for sublimation- or evaporation-inducediodine loss during the spray printing process, the addition of a smallamount (1 at. %) of iodine (I-2) into the CuI precursorsolution was dramatically effective for obtaining CuI films showingthe excellent electrical conductivity of 207.6 S & BULL;cm(-1) and power factor of 673.3 & mu;W & BULL;m(-1)& BULL;K--2,K- resulting in a high zT value of0.31. Importantly, added I-2 played a critical role inincreasing the electrical conductivity by providing iodide to improvethe Cu to I stoichiometry in the CuI films and improve crystallitegrowth. Using 1 at. % I-2 doping, two different flexibleTEGs (one coiled and one foldable) were successfully fabricated thatshowed a high output power density of 236.5 & mu;W & BULL;cm(-2) at a temperature gradient of 22 & DEG;C and high sensitivity tosmall temperature changes induced by a halogen lamp, respectively.This efficient and facile approach to fabricating solution-processabletransparent conductors with high TE performance suggests potentialapplicability to the development of energy-harvesting windows or screens.