Structure, binding energy and optoelectrical properties of p-type CuI thin films: The effects of thickness

•P-type CuI film is prepared by solid iodization evaporated copper.•The exact chemical states of Cu and I is analyzed by XPS spectra.•XPS measurements show the films are pure phase and oxidation state of Cu is +1.•CuI films exhibit ultra-high transparency (95.5%) and good conductivity (34 S/cm).•A CuI/ITO diode structure prepared has good rectification characteristics.