In Situ Construction of a Cs₂SnI₆ Perovskite Nanocrystal/SnS₂ Nanosheet Heterojunction with Boosted Interfacial Charge Transfer

Heterojunction engineering has played an indispensable role in the exploitation of innovative artificial materials with exceptional properties and has consequently triggered a new revolution in achieving high-performance optoelectronic devices. Herein, an intriguing halide perovskite (PVK) and metal dichalcogenide (MD) heterojunction, i.e., a lead-free Cs₂SnI₆ perovskite nanocrystal/SnS₂ nanosheet hybrid, was fabricated in situ for the first time. Comprehensive investigations with experimental characterizations and theoretical calculations demonstrate that cosharing of the Sn atom enables intimate contact in the Cs₂SnI₆/SnS₂ hybrid together with a type II band alignment structure. Additionally, ultrafast carrier separation between SnS₂ and Cs₂SnI₆ has been observed in the Cs₂SnI₆/SnS₂ hybrid by transient absorption measurements, which efficiently prolongs the lifetime of the photogenerated electrons in SnS₂ (from 1290 to 3080 ps). The resultant spatial charge separation in the Cs₂SnI₆/SnS₂ hybrid evidenced by Kelvin probe force microscopy (KPFM) significantly boosts the photocatalytic activity toward CO₂ reduction and the photoelectrochemical performance, with 5.4-fold and 10.6-fold enhancements compared with unadorned SnS₂. This work provides a facile and effective method for the in situ preparation of PVK-MD heterojunctions, which may significantly stimulate the synthesis of various perovskite-based hybrid materials and their further optoelectronic applications.