Engineering Dual p–n-Type CuI with Significant Enhanced Performance for Advanced Thermoelectric Applications

CuI is a well-known thermoelectric (TE) material recognized for its p-type characteristics. However, the development of its n-type counterpart and the integration of both p- and n-type CuI in thermoelectric generators (TEGs) remain largely unexplored. In this study, we successfully tuned the thermoelectric properties of CuI by strategically incorporating Ag, enabling the synthesis of both p-type (Ag_0.2Cu_0.8I) and n-type (Ag_0.9Cu_0.1I) materials using a cost-effective, greener, and scalable successive ionic layer adsorption and reaction (SILAR) method. The p-type Ag_0.2Cu_0.8I exhibited a figure of merit (ZT) of 0.47 at 340 K, driven by a high Seebeck coefficient of 810 μV·K^-1. In contrast, the n-type Ag_0.9Cu_0.1I achieved an exceptional ZT of 2.5 at 340 K, attributed to an ultrahigh Seebeck coefficient of -1891 μV·K^-1. These superior thermoelectric properties make CuI-based materials attractive alternatives to conventional TE materials, such as Bi₂Te₃ and PbTe, which are limited by toxicity and resource scarcity. Furthermore, a prototype thermoelectric glazing unit (5 × 5 cm²) demonstrated a 14 K temperature differential, highlighting its dual functionality in power generation and building heat loss mitigation. These findings underscore the potential of low-cost CuI-based materials for advancing sustainable energy technologies.