Realizing<i>zT</i>>2 in Environment‐Friendly Monoclinic Cu<sub>2</sub>S—Tetragonal Cu<sub>1.96</sub>S Nano‐Phase Junctions for Thermoelectrics
Xiaokun Li, Yue Lou, Kangpeng Jin, Liangwei Fu, Pengfei Xu, Zhan Shi, Tianli Feng, Biao Xu
Abstract
Abstract Phase‐junction nanocomposites, made of nanograins with the same composition but different phases, offer a platform to optimize the physiochemical performance of materials. Herein, we demonstrate a straightforward strategy to synthesize Cu 2− x S phase‐junction nanocomposites by retaining surface 1‐dodecanethiol (DDT) ligands, in contrast to the traditional method that strips the ligands. As a result, phase junctions between a conventional monoclinic (m) phase and an unconventional metastable tetragonal (t) phase are obtained. The significantly improved power factor is obtained due to the doping of the t‐phase. The phase‐junction interfaces reduce thermal conductivity. Finally, surface regulation of phase junctions pushes the peak zT to 2.1 at 932 K, being the highest reported for environment‐friendly metal sulfides. This work provides a paradigm to optimize thermoelectric performance by controlling phase junctions through surface‐ligand tuning.