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

Interlayer charge transfer (CT) basedon band alignment plays avital role in various optoelectronic applications, such as photoluminescencemodulation, superior photoconduction, etc. The layer-by-layer integrationof atomically thin materials with different band alignments is anefficient approach to witness CT. To study interlayer CT, the stackingof 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 annvdW two-dimensional (2D) Bi2O2Se layer overa vdW 2D MoS2 (monolayer) and study the interlayer couplingand CT across the 2D interface. Studies through various spectroscopicand microscopic tools and density functional theory calculations revealthat significant interlayer CT occurs across the heterolayers dueto the favorable band alignment of type-II across the junction. Interestingly,the CT from the 2D Bi2O2Se layer to the monolayerMoS(2) results in photoluminescence (PL) quenching in theMoS(2) layer and enhanced photoconduction in the HS. Low-temperaturePL studies reveal that the robust interlayer coupling between theheterolayers enhances the CT process. The modified Varshni fit revealsthat the electron-phonon coupling constant (Huang-Rhysfactor) is higher for trions (1.13) than for neutral excitons (0.66)in the heterostructure. Upon photoexcitation, the trion-phononcoupling is stronger than the neutral exciton-phonon couplingin the heterostructure system. The additional doping caused by photogeneratedCT was quantified by solving the coupled rate equations using a four-levelmodel, and the results are fully consistent with the CT estimatedfrom the density functional theory (DFT) calculation. These resultsare significant for understanding the interaction between vdW andnvdW 2D heterostructures and further exploration of such 2D heterostructuresin future optoelectronic applications.