Tian Gao, Yi Wen, Shulin Bai, Lizhong Su, H. L. Shi, Rong Liu, Sining Wang, Yixuan Hu, Shibo Liu, Dongrui Liu, Shan Liu, Chao Liang, Xiaokun Feng, Xiaoqian Wang, Yongxin Qin, Xiang Gao, Bingchao Qin, Cheng Chang, Peikang Bai, Li‐Dong Zhao
Thermoelectric power generation requires high dimensionless figure of merit ZT across broad temperatures. The two-dimensional phonon and three-dimensional charge transports enable n-type– Pnma tin selenide (SnSe) crystals to show a peak ZT of ~3.0 at 748 kelvin. In this work, we focused on the high-symmetry Cmcm phase to boost two-dimensional phonon and three-dimensional charge transports and extended the high-performance ( ZT ~ 3.0) plateau. By simultaneously broadening the Cmcm -phase stability window and enhancing lattice symmetry through lead alloying, we extended the high performance from a single temperature point to a wide temperature range of ~250 kelvin in rock salt–like Cmcm SnSe crystals rendered n-type through chlorine doping. An average ZT of ~3.0 was achieved between 673 and 923 kelvin, with a conversion efficiency of ~19.1% under a temperature difference of ~572 kelvin.