2D transition metal dichalcogenides (TMDs) are a promising material system for optoelectronic applications. However, their key figure of merit, the room‐temperature photoluminescence (PL), is extremely low. To overcome this challenge, TMDs need interfacing with other semiconducting materials and discover the underlying physical phenomena. Herein, the optical properties and PL mechanisms of molybdenum disulfide‐organic perylene derivative (PDI/MoS2) based type‐II heterostructures, i.e., PTCDA/MoS2 and PTCDI‐Ph/MoS2, are studied experimentally and theoretically. The PL of MoS2 in PTCDA/MoS2 is enhanced, while a dramatic PL quenching of MoS2 is observed on PTCDI‐Ph/MoS2. The significant radiative PL enhancement of PTCDA/MoS2 is primarily due to the bandgap reduction, high exciton/trion ratio, and epitaxial growth of PTCDA. In contrast, “trap‐like” states in heterointerface, relatively low exciton/trion ratio, and less ordered morphology are responsible for PL quenching of PTCDI‐Ph/MoS2 heterostructure. These findings would provoke a new way to engineer the light‐matter interactions in organic/TMD hybrids, which enables light‐emitting, light‐harvesting applications, and neuromorphic devices.
We report the photoluminescence (PL) characteristics of a van der Waals (vdW) heterojunction constructed by simply depositing an organic semiconductor of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) onto a two-dimensional MoS2 monolayer. The crystallinity of PTCDA on MoS2 is significantly improved due to the vdW epitaxial growth. We observe an enhanced PL intensity and PL peak shift of the MoS2/PTCDA heterojunction compared with the solo MoS2 and PTCDA layer. The synergistic PL characteristics are believed to originate from the hybridization interaction between the MoS2 and the PTCDA as evidenced by density functional theory calculations and Raman measurements. The hybridization interfacial interaction is found to be greatly influenced by the crystalline ordering of the PTCDA film on the 2D MoS2. Our study opens up a new avenue to tune the PL of vdW heterojunctions consisting of TMDs and organic semiconductors for optoelectronic applications.
Graphene nucleation at oxygen-rich Cu sites instead of on the commonly assumed pure Cu surface is discovered using high-spatial-resolution scanning Auger electron microscopy, which reveals a strong O signal existing underneath the graphene seeds, along with density functional theory calculations.
Transition metal dichalcogenides such as MoS2 and WS2 quantum dots (QDs) have been found to show a dramatic enhancement of photoluminescence (PL) quantum efficiency as compared with their planar sheet counterparts. However, the mechanisms of PL enhancement remain not to be very clear. In this work, MoSe2 QDs with the size ranging from about 5.30 nm to 1.55 nm were prepared by a probe-assistant ultrasonication exfoliation approach. The as-prepared MoSe2 QDs are strongly fluorescent, suggesting the existence of quantum confinement effects, and show two distinct PL emissions in the ultraviolet and visible ranges, which are attributed to a band-edge state and a surface related defect state, respectively. We observed blue shifts of the PL peak position and the absorption band edge with the change in the QD size, and the discrepancy of the shifted energies between the PL emission and the estimation based on documented models is briefly addressed.
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