Supercritical Synthesis and Characterization of Graphene–PbS Quantum Dots Composite with Enhanced Photovoltaic Properties

Synthesis of “(aminomethyl)phosphonic acid-functionalized graphene oxide”, and comparison of its adsorption properties for thorium(IV) ion, with plain graphene oxide

The current study presents a simple and scalable method for the synthesis of (aminomethyl)phosphonic acid-functionalized graphene oxide (AMPA-GO) adsorbent. The chemical structure of the new material was disclosed by different instrumental analyses (e.g. FTIR, Raman, XPS, AFM, TEM, XRD, CHN, and UV), and two pertinent mechanisms namely nucleophilic substitution and condensation were suggested for its formation. Adsorption experiments revealed that both AMPA-GO and plain GO have a high affinity toward Th(IV) ions, but the AMPA-GO is superior in terms of adsorption capacity, rate of adsorption, selectivity, pH effect, etc. Indeed, the AMPA-GO can uptake Th(IV) nearly instantaneously, and coexisting Na+ ions have no effect on its adsorption. Thanks to Langmuir isotherm, the maximum adsorption capacities of the GO and AMPA-GO were obtained 151.06 and 178.67 mg g−1, respectively. Interestingly, GO and AMPA-GO both showed a higher preference for thorium over uranium so that the average “K d (Th)/K d (U)” for them was 52 and 44, respectively. This data suggests that chromatographic separation of thorium and uranium is feasible by these adsorbents.

Efficient FAPbI3–PbS quantum dot graphene-based phototransistors

PbS quantum dots capped with formamidinium ligands were deposited as graphene-based photodetectors. Solid phase exchange improves the infrared photo-detectivity.

Solution Processing and Self-Organization of PbS Quantum Dots Passivated with Formamidinium Lead Iodide (FAPbI3)

Solution-processed lead sulfide quantum dots (PbS QDs) are very attractive as NIR-active semiconductors for the fabrication of cost-efficient optoelectronic devices. To control the thin film carrier transport, as well as stability, surface passivation is of crucial importance. Here, we present the successful surface passivation of PbS QDs by the formamidinium lead iodide (FAPbI3) ligand. An effective procedure for the fabrication of FAPbI3-passivated PbS QDs through a binary-phase ligand exchange protocol in hexane and n-methylformamide is demonstrated. It is shown that this solution-processed ligand exchange drastically changes the photoluminescence intensity, exciton recombination dynamics, and carrier lifetime of the nanocrystals. The solution casting of the ligand-exchanged nanocrystals into thin films results in the periodic ordering of QDs in a square superlattice with close contacts. Planar graphene/QD photodetectors fabricated with PbS QDs passivated with FAPbI3 show substantially increased thermal stability as compared to similar devices using PbS QDs passivated with commonly used methylammonium lead iodide.

Cost-Effective and Semi-Transparent PbS Quantum Dot Solar Cells Using Copper Electrodes

PbS quantum dots (QDs) have gained significant attention as promising solution-based materials for third generation of photovoltaic (PV) devices, thanks to their size-tunable band gap, air stability, and low-cost solution processing. Gold (Au), despite its high cost, is the standard electrode in the conventional PbS QD PV architecture because of its perfect alignment with valence levels of PbS QDs. However, to comply with manufacturing requirements for scalable device processing, alternative cost-effective electrodes are urgently required. Here, we employed an interface engineering approach and deposited poly(3-hexylthiophene-2,5-diyl) as a hole transport layer on 1,2-ethanedithiol-capped PbS QDs in order to adjust the valence band of QDs with the work function of inexpensive copper (Cu) electrodes. In fact, this is the first report of a Au-free PbS QD PV system employing the conventional device structure. Our Cu-based device shows a maximum power conversion efficiency (PCE) of 8.7% which is comparable with that of the Au-based device (10.2%). Interestingly, the P3HT-based device shows improved stability with relatively 10% PCE loss after 230 h under continuous illumination. Moreover, using an ultrathin Cu electrode, a semitransparent PbS QD PV is fabricated with a remarkably high average visible transparency of 26% and a PCE of 7.4%.

Synergistic ligand exchange and UV curing of PbS quantum dots for effective surface passivation

Lead sulfide (PbS) quantum dots (QDs) are promising materials in solution-processed photovoltaic (PV) devices due to their tunable bandgap and low-cost processing. Replacing the long oleic acid ligands of the as-synthesized QDs with shorter ligands is a key step for making functional QD PVs with correctly tuned band energies and reduced non-radiative recombination centers. In this work, we study the effect of ultraviolet (UV) treatment of PbS QD layers on the QD surface states during ligand exchange. We demonstrate that this straightforward approach effectively reduces the surface trap states and passivates the surface of QDs. We find that UV treatment reduces the density of hydroxyl groups attached to the QD surface and improves the bonding of short ligands to the QD surface. Multiple analyses show the reduction of nonradiative recombination centers for the UV-treated sample. The power conversion efficiency (PCE) of our optimized PbS QD device reached 10.7% (vs. 9% for the control device) and was maintained above 10% after 230 h of constant illumination.

Infrared tunable, two colour-band photodetectors on flexible platforms using 0D/2D PbS-MoS2 hybrids

Two-dimensional (2D) MoS₂ nanosheets have been integrated with zero-dimensional (0D) PbS quantum dots to achieve a superior optical response extending to the short-wavelength infrared region along with a broadband visible response for multispectral photodetection. The 0D/2D hybrid nanostructures have been synthesized by a one pot, stabilizer-free solvothermal growth process. Microscopic and spectroscopic studies confirmed the formation of PbS QD decorated semiconducting 2H-MoS₂ layers. The size tunable absorption features with longer photo-generated carrier lifetime of synthesized hybrid nanostructures indicate that the integration of PbS QDs in MoS₂ could be a viable approach for fabricating two-colour band photodetectors, viz. visible broadband and wavelength selective short-wave IR photodetectors. Devices have also been demonstrated on polyethylene terephthalate substrates using a solution-based synthesis technique for flexible and ultrathin optoelectronic device applications. The photodetection performance of fabricated devices suggests that the synergic 0D/2D hybrid nanostructures are significantly superior to solution processed hybrid devices operating in the infrared region. The successful integration of 0D QDs in 2D materials may pave the way for novel, high performance, next-generation CMOS compatible flexible photonic devices.

A General Route for Growing Metal Sulfides onto Graphene Oxide and Exfoliated Graphite Oxide

Graphene-based materials are elective materials for a number of technologies due to their unique properties. Also, semiconductor nanocrystals have been extensively explored due to their size-dependent properties that make them useful for several applications. By coupling both types of materials, new applications are envisaged that explore the synergistic properties in such hybrid nanostructures. This research reports a general wet chemistry method to prepare graphene oxide (GO) sheets decorated with nanophases of semiconductor metal sulfides. This method allows the in situ growth of metal sulfides onto GO by using metal dialkyldithiocarbamate complexes as single-molecule precursors. In particular, the role of GO as heterogeneous substrate for the growth of semiconductor nanocrystals was investigated by using Raman spectroscopic and imaging methods. The method was further extended to other graphene-based materials, which are easily prepared in a larger scale, such as exfoliated graphite oxide (EGO).

Evaluation of dosimetric characteristics of graphene oxide/PVC nanocomposite for gamma radiation applications

Graphene oxide-polyvinyl chloride composite was prepared using tetrahydrofuran solvent-assisted dispersion of characterized nano flakes of graphene oxide in polymer matrix. Electrical percolation threshold of GO/PVC nanocomposite was determined via a finite element simulation method with a 2D model and compared with experimental results. A conductive cell with two silver coated walls was designed and fabricated for exploring dosimetric properties of the composite. Some characteristics of the new nanocomposite such as linearity of dose response, repeatability, sensitivity and angular dependence are investigated. According to 2D proposed method, obtained data associated to electrical conductivity of the GO/polymer composite for PVC matrix plotted in different GO weight percentages and had good compatibility (validity) with experimental data. The dose response is linear in the 17–51 mGy dose range and it can be introduced for gamma radiation dosimetry in diagnostic activities.

Synthesis, characterization and biological evaluation of a well dispersed suspension of gallium-68-labeled magnetic nanosheets of graphene oxide for in vivo coincidence imaging

Graphene oxide (GO) nanosheets were hybridized with Fe3O4 nanoparticles (NPs) to form magnetic GO (MGO) and were further labeled by [68Ga]GaCl3 as a potential drug delivery system. Paper chromatography, Fourier transform infra red (FTIR) spectroscopy, low-angle X-ray diffraction (XRD), CHN and atomic force microscopy (AFM) were utilized to characterize the trinary composite ([68Ga]@MGO). Biological evaluations of the prepared nanocomposite were performed in normal Sprague Dawley rats and it was found to be a possible host for theranostic radiopharmaceuticals. The results showed that the grafting of Fe3O4 NPs on nanocomposite reduced the unwanted liver and spleen uptakes and increased the ratio of kidney/liver uptake from 0.037 to 1.07, leading to the fast removal of radioactive agent and less imposed radiation to patients. The high level of hydrogen bonding caused by the presence of functional groups is responsible for this effect. Considering the accumulation of the tracer in vital organs of rat (especially brain), efficient iron oxide grafting, fast wash-out, the short half-life gallium-68 and less imposed radiation doses to patients, this nanocomposite could be a suitable candidate for positron emission tomography (PET) studies and imaging applications.

Chemical processing of three-dimensional graphene networks on transparent conducting electrodes for depleted-heterojunction quantum dot solar cells

The improvement of device performance by using a 3DGN structure as a fast extraction layer for electrons is shown.

Surface passivation of lead sulfide nanocrystals with low electron affinity metals: photoluminescence and photovoltaic performance

Low electron affinity metals like Cd can annihilate deep trap states and increase the current density, resulting in higher performance.

Supercritical synthesis of a magnetite-reduced graphene oxide hybrid with enhanced adsorption properties toward cobalt & strontium ions

The current study presents a supercritical synthesis of magnetite-reduced graphene oxide (M-RGO) in methanol media, in which Fe₃O₄ nanoparticles are simultaneously formed, surface modified and decorated on the surface of the reduced graphene oxide.

Hybrid zinc oxide/graphene electrodes for depleted heterojunction colloidal quantum-dot solar cells

Recently, hybrid nanocomposites consisting of graphene/nanomaterial heterostructures have emerged as promising candidates for the fabrication of optoelectronic devices.