Multiscale Microstructures and Carrier–Phonon Decoupling in BiCuSeO-CDs Composites

Owing to the carrier–phonon coupling, the majority of thermoelectric materials such as BiCuSeO adopt the strategy of sacrificing carrier mobility and thermal properties to improve the electrical performance so as to enhance the zT value. In response, we innovatively introduce carbon dots (CDs) as a nanophase and efficiently synthesize Bi_0.88Ca_0.06Pb_0.06CuSeO-CDs composites, attenuating the carrier–phonon coupling while realizing the structure optimization on the multiscale. The addition of CDs improves the electrical performance (PF_max = 883.99 μW m^–1 K^–2), and CDs introduce multiscale defects that strongly scatter phonons across multiple frequencies, drastically reducing the lattice thermal conductivity to 0.14 W m^–1 K^–1. The BCPCSO-0.15 wt % CDs achieve a record zT value of 1.82 at 873 K, representing a 61.97% enhancement of the BCPCSO matrix, with an average zT value reaching 1.11. This research offers an economical, efficient, and scalable approach to improve thermoelectric performance of BiCuSeO, offering a novel pathway for performance optimization of other structurally similar thermoelectric materials.