Photophysical Dynamics in Semiconducting Graphene Quantum Dots Integrated with 2D MoS₂ for Optical Enhancement in the Near UV

Abstract

The hybrid structure of zero-dimensional (0D) graphene quantum dots (GQDs) and semiconducting two-dimensional (2D) MoS2 has been investigated, which exhibit outstanding properties for optoelectronic devices surpassing the limitations of MoS2 photodetectors where the GQDs extend the optical absorption into the near-UV regime. The GQDs and MoS2 films are characterized by Raman and photoluminescence (PL) spectroscopies, along with atomic force microscopy. After outlining the fabrication of our 0D–2D heterostructure photodetectors comprising GQDs with bulk MoS2 sheets, their photoresponse to the incoming radiation was measured. The hybrid GQD/MoS2 heterostructure photodetector exhibits a high photoresponsivity R of more than 1200 A W–1 at 0.64 mW/cm2 at room temperature T. The T-dependent optoelectronic measurements revealed a peak R of ∼544 A W–1 at 245 K, examined from 5.4 K up to 305 K with an incoming white light power density of 3.2 mW/cm2. A tunable laser revealed the photocurrent to be maximal at lower wavelengths in the near ultraviolet (UV) over the 400–1100 nm spectral range, where the R of the hybrid GQDs/MoS2 was ∼775 A W–1, while a value of 2.33 × 1012 Jones was computed for the detectivity D* at 400 nm. The external quantum efficiency was measured to be ∼99.8% at 650 nm, which increased to 241% when the wavelength of the incoming laser was reduced to 400 nm. Time-resolved measurements of the photocurrent for the hybrid devices resulted in a rise time τrise and a fall time τfall of ∼7 and ∼25 ms, respectively, at room T, which are 10× lower compared to previous reports. From our promising results, we conclude that the GQDs exhibit a sizable band gap upon optical excitation, where photocarriers are injected into the MoS2 films, endowing the hybrids with long carrier lifetimes to enable efficient light absorption beyond the visible and into the near-UV regime. The GQD–MoS2 structure is thus an enabling platform for high-performance photodetectors, optoelectronic circuits, and quantum devices.

Recent Advances in Two-Dimensional Quantum Dots and Their Applications

“…Min et al reported another hybrid structure comprising zero-dimensional (0D) GQDs and semiconducting 2D MoS 2 that exhibits remarkable properties for optoelectronic devices, outperforming MoS 2 photodetectors [146]. GQDs exhibit unique optoelectronic features such as long carrier lifetimes and rapid electron extraction due to enormous transition energies and weak coupling to excitonic states.…”

Graphene quantum dot-porphyrin/phthalocyanine multifunctional hybrid systems: from interfacial dialogue to application

“…[72][73][74][75][76][77][78][79] GQDs have the fascinating characteristics of both two-dimensional (2D) graphene and the exceptional physicochemical properties of QDs, namely, quantum confinement effect, non-zero bandgap, and edge effects. 34,[80][81][82][83] Graphene-based quantum dots (GQDs) have been comprehensively explored due to their desirable attributes such as facile, eco-friendly synthesis, low cost, nontoxicity, good biocompatibility, 36,84,85 high stability, controllable chemical functionality, water dispersibility, surface grafting, stable photoluminescence, 73 robust chemical inertness, 26 excellent electrical, and optical properties, abundant functional groups (e.g., hydroxyl, amino, and carboxyl), electron mobility, and huge surface area, endowing them immense potential applications in the optical, 86 energy, 87 electronic, and biomedical fields. 88,[89][90][91][92][93][94][95][96] Owing to their quantum confinement and special edge effects, GQDs show distinct fluorescent properties and physical and chemical properties.…”

Chlorine Modulation Fluorescent Performance of Seaweed-Derived Graphene Quantum Dots for Long-Wavelength Excitation Cell-Imaging Application

“…Many fluorescent nanomaterials have been developed and used in biomedicine, especially for bioimaging [ 6 , 7 ]. The discovery of semiconductor quantum dots has opened a new chapter in modern fluorescent nanomaterials [ 8 , 9 ]. Compared with traditional organic dyes, the unique advantages of semiconductor quantum dots, such as high quantum yield, excellent photostability, and fluorescence tenability, make them promising materials in bioimaging applications.…”