Band alignment of type-I SnS2/Bi2Se3 and type-II SnS2/Bi2Te3 van der Waals heterostructures for highly enhanced photoelectric responses

Heterostructures based on new advanced materials offer a cornerstone for future optoelectronic devices with improved photoelectric performance. Band alignment is crucial for understanding the mechanism of charge carrier transportation and interface dynamics in heterostructures. Herein, we grew SnS2/Bi2X3 (X = Se, Te) van der Waals heterostructures by combining physical vapor deposition with chemical vapor deposition. The band alignment, measured by high-resolution X-ray photoelectron spectroscopy, suggested the successful design of type-I SnS2/Bi2Se3 and type-II SnS2/Bi2Te3 heterostructures. The SnS2/Bi2X3 heterostructure greatly improved the photoelectric response of a photoelectrochemical-type photodetector. The photocurrent densities in the type-I SnS2/Bi2Se3 and type-II SnS2/Bi2Te3 heterostructure-based devices were more than one order of magnitude higher than those of SnS2, Bi2Se3, and Bi2Te3. The improved photoelectric properties of the SnS2/Bi2X3 heterostructures can be explained as follows: (i) the photoexcited electrons and holes are effectively separated in the heterostructures; (ii) the charge-transfer efficiency and carrier density at the interface between the SnS2/Bi2X3 heterostructures and the electrolyte are greatly improved; (iii) the formed heterostructures expand the light absorption range. The photoelectric performance was further enhanced by efficient light trapping in the upright SnS2. The photoelectric response is higher in the type-I SnS2/Bi2Se3 heterostructure than in the type-II SnS2/Bi2Te3 heterostructure due to more efficient charge transportation at the type-I SnS2/Bi2Se3 heterostructure/electrolyte interface. These results suggest that suitable type-I and type-II heterostructures can be developed for high-performance photodetectors and other optoelectronic devices.