When energy and information revolutions meet 2D Janus

The depletion of energy sources, worsening environmental issues, and the quantum limitations of integrated circuits for information storage in the post-Moore era are pressing global concerns. Fortunately, two-dimensional (2D) Janus materials, possessing broken spatial symmetry, with emerging non-linear optical response, piezoelectricity, valley polarization, Rashba spin splitting, and more, have established a substantial platform for exploring and applying modifiable physical, chemical, and biological properties in materials science and offered a promising solution for these energy and information issues. To provide researchers with a comprehensive repository of the 2D Janus family, this review systematically summarizes their theoretical predictions, experimental preparations, and modulation strategies. It also reviews the recent advances in tunable properties, applications, and inherent mechanisms in optics, catalysis, piezoelectricity, electrochemistry, thermoelectricity, magnetism, and electronics, with a focus on experimentally realized hexagonal and trigonal Janus structures. Additionally, their current research state is summarized, and potential opportunities and challenges that may arise are highlighted. Overall, this review aims to serve as a valuable resource for designing, fabricating, regulating, and applying 2D Janus systems, both theoretically and experimentally. This review will strongly promote the advanced academic investigations and industrial applications of 2D Janus materials in energy and information fields.