Hinge-like structure induced unusual properties of black phosphorus and new strategies to improve the thermoelectric performance

Guangzhao Qin¹ , Qing-Bo Yan¹ , Zhenzhen Qin² , Sheng-Ying Yue³ , Hui-Juan Cui³ , Qing-Rong Zheng³ & Gang Su^{3 1}

College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China, 2 College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071, People’s Republic of China, 3 School of Physics, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China.

We systematically investigated the geometric, electronic and thermoelectric (TE) properties of bulk black phosphorus (BP) under strain. The hinge-like structure of BP brings unusual mechanical responses such as anisotropic Young’s modulus and negative Poisson’s ratio. A sensitive electronic structure of BP makes it transform among metal, direct and indirect semiconductors under strain. The maximal figure of merit ZT of BP is found to be 0.72 at 800 K that could be enhanced to 0.87 by exerting an appropriate strain, revealing BP could be a potential medium-high temperature TE material. Such strain-induced enhancements of TE performance are often observed to occur at the boundary of the direct-indirect band gap transition, which can be attributed to the increase of degeneracy of energy valleys at the transition point. By comparing the structure of BP with SnSe, a family of potential TE materials with hinge-like structure are suggested. This study not only exposes various novel properties of BP under strain, but also proposes effective strategies to seek for better TE materials.