Interlayer Charge-Transfer-Induced Photoluminescence Quenching and Enhanced Photoconduction in Two-Dimensional Bi₂O₂Se/MoS₂ Type-II Heterojunction

Interlayer charge transfer (CT) based on band alignment plays a vital role in various optoelectronic applications, such as photoluminescence modulation, superior photoconduction, etc. The layer-by-layer integration of atomically thin materials with different band alignments is an efficient approach to witness CT. To study interlayer CT, the stacking of ultrathin van der Waals (vdW) materials has been studied extensively, while the stacking of vdW materials with non-van der Waals (nvdW) materials is least explored. Herein, we present the stacking of an nvdW two-dimensional (2D) Bi 2 O 2 Se layer over a vdW 2D MoS 2 (monolayer) and study the interlayer coupling and CT across the 2D interface. Studies through various spectroscopic and microscopic tools and density functional theory calculations reveal that significant interlayer CT occurs across the heterolayers due to the favorable band alignment of type-II across the junction. Interestingly, the CT from the 2D Bi 2 O 2 Se layer to the monolayer MoS 2 results in photoluminescence (PL) quenching in the MoS 2 layer and enhanced photoconduction in the HS. Low-temperature PL studies reveal that the robust interlayer coupling between the heterolayers enhances the CT process. The modified Varshni fit reveals that the electron–phonon coupling constant (Huang–Rhys factor) is higher for trions (1.13) than for neutral excitons (0.66) in the heterostructure. Upon photoexcitation, the trion–phonon coupling is stronger than the neutral exciton–phonon coupling in the heterostructure system. The additional doping caused by photogenerated CT was quantified by solving the coupled rate equations using a four-level model, and the results are fully consistent with the CT estimated from the density functional theory (DFT) calculation. These results are significant for understanding the interaction between vdW and nvdW 2D heterostructures and further exploration of such 2D heterostructures in future optoelectronic applications.