Thermoelectric and Optical Properties of Nanostructured p-Type CuI Thin Films Grown by Glancing Angle Deposition for Transparent Energy-Harvesting Applications

Copper iodide (CuI) is recognized as a promising p-type transparent material with excellent thermoelectric properties. CuI thin films are typically produced by depositing a copper layer, followed by iodination. However, this process poses challenges in controlling the film's structure, often leading to excessive grain growth in CuI and reduced optical clarity due to increased light scattering from larger grains. In our study, we introduce an innovative method to regulate the structural characteristics of CuI films by employing the glancing angle deposition (GLAD) technique in depositing the initial copper layer. This method creates nanostructured copper films that guide the formation of CuI grains during vapor iodination. By varying the deposition angle and iodination time, we adjust the size and shape of the synthesized CuI nanostructure-sized grains. This directly enhances the thermoelectric properties and the transmittance of the CuI films. We observe that our CuI films result in a 43% increase in Seebeck coefficient (S) of 352 μV/K, leading to a 90% enhancement at room temperature with a power factor of 339 μW/mK2 compared to the previously reported CuI prepared by the vapor iodination method. Additionally, these nanostructured films exhibit high transparency with a transmittance of 85% at a 560 nm wavelength, demonstrating superior optical properties at this wavelength. These results highlight the potential for integrating nanostructured p-type transparent materials into smart windows and cooling systems for optical chips.