2D Graphene-Like Pb-Free Perovskite Semiconductor CsSb(BrI) with Quasi-linear Electronic Dispersion and Direct Bandgap Close to Germanium.

Thanks to its ultrahigh carrier mobility (∼10-10 cm V s), graphene shows tremendous application potential in nanoelectronics, but it cannot be applied in effective field-effect transistors (FETs) because of its intrinsic gapless band structure. Thus, introducing a bandgap for graphene is a prerequisite to realize an FET for logic applications. Herein, through first-principles GW calculations, we have predicted a series of novel Dion-Jacobson (DJ) phase halide perovskite semiconductors CsSb(BrI) ( = 0, 0.5, 1) with the quasi-linear (graphene-like) band edge dispersion; as the best one of which, CsSbBrI exhibits a direct bandgap (0.52 eV) as well as a quasi-linear electronic dispersion, yielding an ultrasmall carrier effective mass (0.03 ) and a high estimated carrier mobility (5 × 10 cm V s). This gives a significant reference to the exploration of semiconductors with excellent transport properties. Moreover, our calculations also implicate that the DJ perovskites CsSb(BrI) ( = 0, 0.25, 0.5, 0.75, 1) show soft and anisotropic mechanical characteristics as well as excellent electronic, transport, and optical properties, which demonstrate their multifunctional application in infrared optoelectronic, high-speed electronics, and photovoltaics.