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 <i>zT</i> 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_<i>max</i> = 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 <i>zT</i> value of 1.82 at 873 K, representing a 61.97% enhancement of the BCPCSO matrix, with an average <i>zT</i> 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.