Synthesis and Applications of Wide Bandgap 2D Layered Semiconductors Reaching the Green and Blue Wavelengths

Two-dimensional semiconductors with a layered structure are now among the most extensively studied materials. The unique structural form of 2D layered semiconductors provides several benefits over other existing materials as key components in next-generation nanodevices such as transistors, photodetectors, solar cells, light emitting devices, molecular sensors, and optical imaging sensors. However, most of these studies concentrate on narrow bandgap semiconductors (bandgap Eg < 2 eV) that emit/absorb in the red and infrared regions. Recently, more research has focused on wide bandgap 2D layered semiconductors, as they have demonstrated great potential in applications in electronics and optoelectronics for the green and blue wavelength regions. This Review summarizes the 2D layered materials that have been experimentally proven as wide bandgap semiconductors, including GaS, GaSe, InSe, SnS2, GeS2, GeSe2, HfS2, PbI2, Ruddlesden–Popper perovskites, MoO3, V2O5, Sr2Nb3O10, etc. We first provide a brief introduction of the crystal structure of the above-mentioned wide bandgap 2D materials. Second, various strategies for bandgap modulation are outlined to demonstrate the powerful tunability of 2D semiconductors from structure to properties, such as number of layers, strain, defects and doping, and alloying. Third, we summarize the current prevailing growth methods and techniques developed to synthesize such a wide range of materials, including exfoliation, vapor phase deposition, solution phase synthesis, and two-step growth. We then highlight some of the exciting applications relating to their wide bandgaps in electronics, photodetectors, solar cells, light emitting diodes, and photoelectrochemical catalysis. Finally, we provide our perspectives on the current challenges and future development in this field.