Thermoelectric and\nOptical Properties of Nanostructured\np‑Type CuI Thin Films Grown by Glancing Angle Deposition for\nTransparent Energy-Harvesting Applications

Copper iodide (CuI)\nis recognized as a promising p-type\ntransparent\nmaterial with excellent thermoelectric properties. CuI thin films\nare typically produced by depositing a copper layer, followed by iodination.\nHowever, this process poses challenges in controlling the film’s\nstructure, often leading to excessive grain growth in CuI and reduced\noptical clarity due to increased light scattering from larger grains.\nIn our study, we introduce an innovative method to regulate the structural\ncharacteristics of CuI films by employing the glancing angle deposition\n(GLAD) technique in depositing the initial copper layer. This method\ncreates nanostructured copper films that guide the formation of CuI\ngrains during vapor iodination. By varying the deposition angle and\niodination time, we adjust the size and shape of the synthesized CuI\nnanostructure-sized grains. This directly enhances the thermoelectric\nproperties and the transmittance of the CuI films. We observe that\nour CuI films result in a 43% increase in Seebeck coefficient (<i>S</i>) of 352 μV/K, leading to a 90% enhancement at room\ntemperature with a power factor of 339 μW/mK<sup>2</sup> compared\nto the previously reported CuI prepared by the vapor iodination method.\nAdditionally, these nanostructured films exhibit high transparency\nwith a transmittance of 85% at a 560 nm wavelength, demonstrating\nsuperior optical properties at this wavelength. These results highlight\nthe potential for integrating nanostructured p-type transparent materials\ninto smart windows and cooling systems for optical chips.