Graphene quantum dots (GQDs) have drawn much interest in recent years because of their distinctive qualities, including cheap cost, mass manufacturing, improved biocompatibility, strong water solubility and highly controllable photoluminescence (PL). Due to their notable electrical and optical features, graphene quantum dots are among the most essential zero-dimensional materials. Creating multiple layers and the graphene quantum dots' small size of less than 30 nm makes them unique. Due to its excellent fluorescence behavior, the charge generated by the quantum confinement effect, and the edge effect, graphene quantum dots also attracted interest for optoelectronic applications.
The development of quantum dots' dispersion in the polymer matrix is a crucial topic that has received much research. For example, quantum dots may be included in polymeric matrices to improve stability and prevent aggregation. In addition, it displays a diverse range of absorption spectra from UV to visible wavelengths. Furthermore, graphene quantum dots are anticipated to exhibit greater biocompatibility compared to other inorganic semiconductor nanoparticles. Studying the photoresponsive characteristics of conducting polymer-GQDs nanocomposites is crucial.
Polypyrrole (PPy)
Polypyrrole (PPy) is a special conducting polymer with good charge transfer resistance, large electron affinity, low ionization potential, high electrical conductivity, mass manufacturing, cheap cost and straightforward synthesis. It is a conjugated polymer that is stable in the environment and exhibits great visual absorption. However, polypyrrole uses are constrained because of their poor processability, mechanical attributes, and solubility.
Since the carbon material exhibits better electrochemical, electrical and mechanical capabilities than the conducting polymers alone, the modification of conductive polymer with carbon-based material is crucial for a broad range of applications, including energy storage, catalysis, and sensors.
Inorganic colloidal quantum dots offer greater environmental durability, superior optical characteristics, and significant promise for composites that have shown high-performance UV photodetectors at cheap cost with simple manufacture. In this study, researchers show how to easily and inexpensively produce the Polypyrrole-Graphene Quantum Dots (PPy-GQD) composite using a chemical oxidation polymerization technique.
Graphene Quantum Dots Synthesis
The one-step hydrothermal approach was used to produce the graphene quantum dots. First, 100 mL of deionized water was used to dissolve 3 wt% of glucose powder completely, and then the mixture was sonicated for 20 minutes. The final product's color changed from translucent to light yellow after being cooked at 180 °C for three hours in a 100 mL Teflon-lined stainless steel autoclave. The yellow solution produced after centrifuging the prepared solution for 30 minutes at 3000 rpm contains graphene quantum dots.
Polypyrrole-Graphene Quantum Dots Composite Synthesis
With constant stirring, 100 mL of 1 M HCl was combined with a 0.3 M pyrrole monomer and 0.7 M FeCl3 solution. The solution was supplemented with 20 and 40 mL of graphene quantum dots, and the mixture was then heated at 60 °C for 20 min. This solution was mixed with 100 mL of 0.7 M FeCl3, centrifuged after 15 minutes, and produced PPy-GQDs (PGC) composites. The polypyrrole's 20 and 40 mL graphene quantum dots were designated as PGC2 and PGC4, respectively.
Single Layer Device Fabrication
The ultrasonically cleaned ITO-coated glass substrates were washed in deionized water after being cleaned in acetone and methanol for 10 minutes at 27 °C and were dried using 99.9999% pure nitrogen gas.
The PPy-GQDs active layer was applied on ITO using a simple brush coating and cured for 15 minutes at 60 °C. A doctor blade approach was used on the device's top to apply the silver paste; its effective area was 1 cm2. Under UV light, the manufactured device with thicknesses of 84.7 nm (PGC4) and 91.3 nm (PGC2) was evaluated for cyclic voltammetry and IT measurement.
To highlight the physical and chemical characteristics of the synthesized composite nanostructure GQDs-based novel UV photodetector device, several measurements were then carried out, including the energy level diagram, Mott Schottky plot, device photoresponse and photocurrent, transmission electron microscopy (TEM), cyclic voltammetry (CV), photoluminescence (PL), UV-visible absorption, X-ray diffraction (XRD) and FT-IR.
Significant Findings of the Study
The hydrothermal process was used to create highly luminous graphene quantum dots. Polypyrrole-graphene quantum dots composites were created using a chemical oxidation polymerization method. The crystal fringes in the transmission electron microscopy picture and the FT-IR data indicated that the graphene quantum dots were evenly distributed over the polypyrrole surface. The photoluminescence verified that the π-conjugation interaction between polypyrrole and graphene quantum dots is what causes the composite's redshift. The new photodetector strongly responds to 355 nm UV light, 2.33 μA/W in PGC4 composite.
By using polypyrrole-graphene quantum dots composites in high-performance, affordable UV photodetectors, there are now more opportunities than ever before due to the decreased carrier transportation barrier brought about by the improved responsivity compared to PGC2 (1.93 μA/W), which also led to excellent stability and reproducibility, quick response times, and highly durable devices. In the future, the hybrid photodetector device's stable monolayer of active material can be established via further research for various wavelengths.
Reference
Molahalli Vandana, Hundekal Devendrappa, Paola De Padova and Gurumurthy Hegde (2022) Polymer Nanocomposite Graphene Quantum Dots for High-Efficiency Ultraviolet Photodetector. Nanomaterials. https://www.mdpi.com/2079-4991/12/18/3175/htm
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