Thermoelectric properties of Ga-doped ZnO produced via a green synthesis method

GaxZn1-xO (x = 0, 0.01, and 0.02) nanoparticles were synthesized via a simple, low-cost, and ecofriendly method using orange peel extract as a stabilizing agent. Research on such green synthesis approaches for Ga-doped ZnO remains limited. The crystal structure and thermoelectric properties of the samples were investigated. Gallium (Ga) doping improved the crystal structure and temperature-dependent electrical conductivity of ZnO. In particular, the Ga-doped ZnO sample with 2 at.% Ga (GZO-2) exhibited an electrical conductivity nearly 30 times higher than that of undoped ZnO at 1068 K. Furthermore, the power factor of this sample reached approximately 56 mW/mK2 at 1068 K, nearly twofold higher than that of undoped ZnO. Additionally, the reduced grain size enhanced grain boundary scattering, markedly decreasing thermal conductivity. Therefore, GZO-2 exhibited the highest figure of merit, approximately 2.5 times higher than that of undoped ZnO. These results highlight the novelty of using agricultural-waste-derived orange peel extract in green synthesis and demonstrate the effectiveness of Ga doping in enhancing the thermoelectric performance of ZnO through microstructural modification.