Atomistic insights into optoelectronic properties of tin halide perovskite CsSnCl3/Cs2SnCl6 hetero-interfaces

Low-toxicity tin halide perovskites (ASnX(3)) with excellent optoelectronic properties are attracting an increasing level of interest. Sn2+ oxidation to Sn4+ via forming Sn vacancies should promote the formation of A(2)SnX(6). The resulted Cs2SnCl6/CsSnCl3 hetero-interfaces can have significant influence on the optoelectronic properties. Here, we performed first-principles calculations to explore the electronic and optical properties of Cs2SnCl6/CsSnCl3 hetero-interfaces. Our results revealed that the bandgap of Cs2SnCl6/CsSnCl3 is significantly reduced due to the type-II band alignment with the VBM and CBM states are respectively dominated by CsSnCl3 and Cs2SnCl6. Both frontier states are derived from antibonding states of Sn 5s and Cl 3p, thus exhibit rather similar orbital hybridization characters. Spontaneous spacial separation of photo-excited charge carriers and electron tunneling are expected to occur at Cs2SnCl6/CsSnCl3 interfaces, which should be beneficial to increased carrier density and long carrier lifetime. The CBM state exhibits rather high localization due to the effective zero-dimensional electronic structure of Cs2SnCl6. Moreover, Cs2SnCl6/CsSnCl3 superlattices exhibit improved light absorption. The electronic and optical properties of Cs2SnCl6/CsSnCl3 can be well modulated by varying the thickness of either perovskite layer. Our work provides theoretical insights into the optoelectronic properties of Cs2SnCl6/CsSnCl3 heterostructures, shedding light on the regulation strategies for high-performance tin halide perovskite optoelectronics.