In the present paper, a CuI nanoparticle was grown in a polyvinyl alcohol (PVA) solution using tetramethylethylenediamine (TMEDA) as a crystal growth inhibitor. The effect of TMEDA on the structural, optical and electrochemical properties of CuI/PVA was investigated using X-ray diffraction (XRD), a scanning and transmission electron microscopy, UV–Vis spectroscopy, and cyclic voltammetry techniques. XRD showed the growth of CuI nanoparticles to about 10 nm in size for higher CuI concentrations (10 wt %). Optical absorption showed a direct transition, with direct optical band gap values decreasing from 1.6 to 1.5 and from 1.62 to 1.5 eV for colloidal and solid films, respectively. Cyclic voltammetry measurements have been conducted to ascertain the position of both the HOMO and LUMO levels, and the chemical band gap was found in the range 2.58–3.30 eV with varying CuI concentration.