Oxygen incorporation effects on the structural and thermoelectric properties of copper(I) iodide

Oxygen is a ubiquitous contaminant in thin films grown in high vacuum systems, and it was hypothesized to play an important role in the properties of the p-type conductivity of transparent copper(I) iodide, CuI. We study the ambient properties of CuI deposited at various partial pressures of oxygen gas. Through a variety of experimental techniques, we find that achieving a critical oxygen partial pressure of below p(O2) = 3×10−5 mbar is essential for depositing stoichiometric and conductive CuI thin films. Notably, we relate the commonly reported copper excess to the presence of oxygen within the CuI films. Notably, we relate the commonly reported excess of copper in CuI thin films to to the presence of oxygen. Finally, we infer from transport and optical measurements that the hole transporting properties of sputtered CuI films are dominated by an abundance of VCu defects with an acceptor transition energy of 84±3 meV rather than OI defects with an acceptor transition energy of 175±14 meV.