Applications of polymorphic two-dimensional transition metal dichalcogenides in electronics and optoelectronics

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are a typical class of 2D materials with promising potential for future electronics and optoelectronics. Moreover, the rich crystal structures provide polymorphic TMDs with distinct phase-dependent physicochemical properties. Therefore, it would be fascinating to achieve controllable growth and phase transformation of TMDs via phase engineering and utilize them in various application fields. Nowadays, significant efforts have been made to combine the distinct properties of TMD polymorphs to improve device performance and find novel applications. For example, TMDs with metallic phases, such as 1T-MoS₂ and 1T'-MoTe₂, have been widely utilized as electrodes to achieve ultra-low contact resistance in TMD-based transistors. The resistance changes with the reversible phase transformation also make TMDs attractive for memory devices and emerging neuromorphic computing. This chapter summarizes the recent advances in electronic and optoelectronic applications of TMDs with various polymorphs, including field-effect transistors (FETs), memories, energy harvesting devices, photodetectors, and solar cells. We demonstrate the phase-dependent properties of polymorphic TMDs and discuss the role of different TMD phases in electronic and optoelectronic devices.