Entropy-Boosting Intrinsic Elemental Disorder for Advanced Thermoelectric Performance in MoSSe

Entropy design, facilitated by disorder, emerges as a crucial strategy for the performance enhancement of thermoelectric materials. The characteristic average multielement composition of Janus MoSSe offers an opportunity to introduce intrinsic elemental disorder by altering the positions of different atoms, thereby boosting entropy. Here, we explored the thermoelectric performance of the initial MoSSe and various constructed disordered structures through first-principles calculations. The results demonstrated that the intrinsic elemental disorder enables simultaneous optimization of power factor and reduction of thermal conductivity, with the optimal disordered structure achieving a ZT of 2.89 at 700 K, approximately 10 times greater than the initial structure. Atomic disorder directly induces charge disorder, decreasing the polarity and enhancing the charge density of the valence band maximum (VBM) to optimize conductivity. This leads to local atomic energy level resonances, which significantly increase the electronic density of states, enhancing the Seebeck coefficient. Moreover, the disorder considerably intensifies phonon scattering through the compression of phonon bandgap and the increased number of peaks for phonon density of states. The lowest thermal conductivity of the disordered structures reaches 1.02 W·m^-1·K^-1 at 700 K. Comprehensive analyses were carried out through the examination of phonon lifetime, phonon group velocity, and specific heat. Finally, we quantified structural disorder utilizing entropy and derived thermoelectric performance optimization based on the intrinsic elemental disorder of the Janus materials. Our results demonstrate how control over intrinsic elemental disorder offers an effective avenue for tuning the performance of thermoelectric materials.