FET-based charge carrier mobility measurements in low-conductivity materials, as well as semiconductor materials with a high density of trapping states, such as nanocrystals and polycrystalline films, are highly distorted due to charge accumulation in the transistor structure. In this work, a comparative study of the measurement of the mobility of charge carrier in conductive polymers, nanocrystals and polycrystalline films, using the analysis of output and transfer characteristics, was carried out. It is shown that using output characteristics instead of transfer characteristics for calculating the charge carrier mobility helps to avoid a systematic error in the measurement. Keywords: field-effect transistor, FET, charge carrier mobility, output characteristics, transfer characteristics, charge accumulation, nanocrystals.

Lead chalcogenide nanocrystals (NCs) are an emerging class of photoactive materials that have become a versatile tool for fabricating new generation photonics devices operating in the near-IR spectral range. NCs are presented in a wide variety of forms and sizes, each of which has its own unique features. Here, we discuss colloidal lead chalcogenide NCs in which one dimension is much smaller than the others, i.e., two-dimensional (2D) NCs. The purpose of this review is to present a complete picture of today’s progress on such materials. The topic is quite complicated, as a variety of synthetic approaches result in NCs with different thicknesses and lateral sizes, which dramatically change the NCs photophysical properties. The recent advances highlighted in this review demonstrate lead chalcogenide 2D NCs as promising materials for breakthrough developments. We summarized and organized the known data, including theoretical works, to highlight the most important 2D NC features and give the basis for their interpretation.

Lead chalcogenide nanoplatelets (NPLs) have emerged as a promising material for devices operating in the near IR and IR spectrum region. Here, we first apply the cation exchange method to PbSe/PbS core/shell NPL synthesis. The shell growth enhances NPL colloidal and environmental stability, and passivates surface trap states, preserving the main core physical properties. To prove the great potential for optoelectrical applications, we fabricate a photoconductor using PbSe/PbS NPLs. The device demonstrates enhanced conductivity and responsivity with fast rise and fall times, resulting in a 13 kHz bandwidth. The carrier transport was investigated with the field effect transistor method, showing p-type conductivity with charge mobility of 1.26 × 10−2 cm2·V−1·s−1.

FET-based charge carrier mobility measurements in low-conductivity materials, as well as semiconductor materials with a high density of trapping states, such as nanocrystals and polycrystalline films, are highly distorted due to charge accumulation in the transistor structure. In this work, a comparative study of the measurement of the mobility of charge carrier in conductive polymers, nanocrystals and polycrystalline films, using the analysis of output and transfer characteristics, was carried out. It is shown that using output characteristics instead of transfer characteristics for calculating the charge carrier mobility helps to avoid a systematic error in the measurement.

Nowadays nanostructures are in demand in various fields from biomedicine to green energy. Photoluminescence (PL) spectral measurements are a powerful tool to study nanomaterials unique physical and optical properties. Most modern spectral approaches are associated with the study of a sample on a substrate or in colloidal solution. In turn, we propose a technique for studying the luminescence of a single object levitating in a quadrupole Paul trap. To verify the technique, we investigate PL spectra of individual trapped charged microcluster of CdSe/ZnS quantum dots. The results obtained open prospects of optical research on single particles isolated from the environment.

Today, the development of nanomaterials with sensing properties attracts much scientific interest because of the demand for low-cost nontoxic colloidal nanoprobes with high sensitivity and selectivity for various biomedical and environment-related applications. Carbon dots (CDs) are promising candidates for these applications as they demonstrate unique optical properties with intense emissions, biocompatibility, and ease of fabrication. Herein, we developed synthesis protocols to obtain CDs based on o-phenylenediamine with a variety of optical responses depending on additional precursors and changes in the reaction media. The obtained CDs are N-doped (N,S-doped in case of thiourea addition) less than 10 nm spherical particles with emissions observed in the 300–600 nm spectral region depending on their chemical composition. These CDs may act simultaneously as absorptive/fluorescent sensing probes for solvent polarity with ∆S/∆ENT up to 85, for ∆ENT from 0.099 to 1.0 and for pH values in the range of 3.0–8.0, thus opening an opportunity to check the pH in non-pure water or a mixture of solvents. Moreover, CDs preserve their optical properties when embedded in cellulose strips that can be used as sensing probes for fast and easy pH checks. We believe that the resulting dual-purpose sensing nano probes based on CDs will have high demand in various sensing applications.

Near-IR semiconductor colloidal nanoplatelets (NPs) are a new and promising class of materials for the development of photodetectors because they can effectively absorb visible and infrared optical radiation. In this work, we study the photoconductivity of HgTe colloidal nanoplatelets with ligands of 1,2-ethanedithiol and tetrabutylammonium iodide. It has been shown that the choice of ligands is a key factor in achieving high operational characteristics. It has been shown that the photoconductivity sensitivity reaches 0.995 and the specific detectivity reaches 1.2·10 9 J Jones when 1,2-ethadithiol is used as ligands. Keywords: Near-IR, photodetectors, specific detectivity, EDT, TBAI.

The field-effect transistor method is used to study the mobility of charge carriers in layers of lead sulfide nanocrystals with ligands of tetrabutylammonium iodide and 1,2-ethanedithiol used to create solar cells. The difference between the operating of a transistor in ambient air and in an inert atmosphere is demonstrated. It is shown that, in the ambient air, the processes of charging nanocrystals are activated when current flows, and the influence of the polarization of the interface of nanocrystals and the insulator on the measurement of the mobility is analyzed. Different reactions of the layers with ligands to light have been demonstrated, showing a significant oxidation of the surface of nanocrystals treated with 1,2-ethanedithiol.

Semiconductor 2D nanostructures are a new platform for the creation of modern optoelectronic devices. Layered 2D PbSe-MoS2 nanostructures with efficient photoinduced charge transfer from PbSe nanoplatelets (NPLs) to MoS2 were created. When PbSe NPLs with short organic ligands are deposited onto a thin layer of MoS2 NPLs, a decrease in their photoluminescence intensity and a decrease in the average photoluminescence lifetime are observed. When a layered 2D PbSe-MoS2 nanostructure is illuminated with IR radiation, a photocurrent appears, which indicates the contribution of PbSe NPLs to the electrical response of the system. Ultrathin layers of transition metal dichalcogenides sensitized with nanostructures based on lead chalcogenides can be used in photodetectors with a spectral sensitivity region extended to the near-IR range. Keywords: nanoplatelets, transition metal dichalcogenides, charge transfer, near infrared region.

Semiconductor 2D nanostructures are a new platform for the creation of modern optoelectronic devices. Layered 2D PbSe-MoS2 nanostructures with efficient photoinduced charge transfer from PbSe nanoplatelets (NPLs) to MoS2 were created. When PbSe NPLs with short organic ligands are deposited onto a thin layer of MoS2 NPLs, a decrease in their photoluminescence intensity and a decrease in the average photoluminescence lifetime are observed. When a layered 2D PbSe-MoS2 nanostructure is illuminated with IR radiation, a photocurrent appears, which indicates the contribution of PbSe NPLs to the electrical response of the system. Ultrathin layers of transition metal dichalcogenides sensitized with nanostructures based on lead chalcogenides can be used in photodetectors with a spectral sensitivity region extended to the near-IR range.

Doping the semiconductor nanocrystals is one of the most effective ways to obtain unique materials suitable for high-performance next-generation optoelectronic devices. In this study, we demonstrate a novel nanomaterial for the near-infrared spectral region. To do this, we developed a partial cation exchange reaction on the HgTe nanoplatelets, substituting Hg cations with Pb cations. Under the optimized reaction conditions and Pb precursor ratio, a photoluminescence band shifts to ~1100 nm with a quantum yield of 22%. Based on steady-state and transient optical spectroscopies, we suggest a model of photoexcitation relaxation in the HgTe:Pb nanoplatelets. We also demonstrate that the thin films of doped nanoplatelets possess superior electric properties compared to their pristine counterparts. These findings show that Pb-doped HgTe nanoplatelets are new perspective material for application in both light-emitting and light-detection devices operating in the near-infrared spectral region.

The field-effect transistor method is used to study the mobility of charge carriers in layers of lead sulfide nanocrystals with ligands of tetrabutylammonium iodide and 1,2-ethanedithiol used to create solar cells. The difference between the operating of a transistor in ambient air and in an inert atmosphere is demonstrated. It is shown that, in the ambient air, the processes of charging nanocrystals are activated when current flows, and the influence of the polarization of the interface of nanocrystals and the insulator on the measurement of the mobility is analyzed. Different reactions of the layers with ligands to light have been demonstrated, showing a significant oxidation of the surface of nanocrystals treated with 1,2-ethanedithiol. Keywords: solar cells, trap states, photoconductivity.

Surface-enhanced Raman spectroscopy (SERS) is regarded as a versatile tool for studying the composition and structure of matter. This work has studied the preparation of a SERS substrate based on a self-assembling plasmonic nanoparticle film (SPF) in a polymer matrix. Several synthesis parameters for the SPF are investigated, including the size of the particles making up the film and the concentration and type of the self-assembling agent. The result of testing systems with different characteristics is discussed using a model substance (pseudoisocyanin iodide). These models can be useful in the study of biology and chemistry. Research results contain the optimal parameters for SPF synthesis, maximizing the SERS signal. The optimal procedure for SPF assembly is determined and used for the synthesis of composite SPFs within different polymer matrices. SPF in a polymer matrix is necessary for the routine use of the SERS substrate for various types of analytes, including solid samples or those sensitive to contamination. Polystyrene, polyvinyl alcohol (PVA), and polyethylene are investigated to obtain a polymer matrix for SPF, and various methods of incorporating SPF into a polymer matrix are being explored. It is found that films with the best signal enhancement and reproducibility were obtained in polystyrene. The minimum detectable concentration for the SERS substrate obtained is equal to 10−10 M. We prepared a SERS substrate with an analytical enhancement factor of 2.7 × 104, allowing an increase in the detection sensitivity of analyte solutions of five orders of magnitude.

We studied self-assembled plasmonic films (SPF) based on gold nanoparticles (Au-NPs). We recorded the intensity distribution maps (IDM) with an area of 2025 μm2 (9 × 9 points). We have observed uniform enhancement across the entire surface of SPF. Therefore, we used the parameters average intensity of IDM and IDM gate when we optimized the synthesis of SPF. Average intensity is the average intensity value over 81 spectra of the IDM. The gate is the span excluding 10% of the outliers. We have discovered that the maximum average intensity was observed at a concentration of 1.00 × 10–5 M. A decrease in the concentration of Au-NPs leads to a decrease in the average intensity. A simultaneous decrease in TOABr and A-u‑NPs concentration also leads to a decrease in the average intensity. The film obtained by the optimal synthesis method was characterized using SEM and AFM.

We report the creation of layered 2D PbSe-MoS2 nanostructures which demostrate efficient electron transfer from PbSe nanoplatelet to MoS2 nanoplatelet. Charge transfer was confirmed by means of Results of the work show that ultrathin layers of transition metal dichalcogenides sensitized by 2D lead chalcogenide nanostructures can be effectively used in photodetectors with a spectral sensitivity extended to the near-IR range.

Near-IR semiconductor colloidal nanoplatelets (NPs) are a new and promising class of materials for the development of photodetectors because they can effectively absorb visible and infrared optical radiation. In this work, we study the photoconductivity of HgTe colloidal nanoplatelets with ligands of 1,2-ethanedithiol and tetrabutylammonium iodide. It has been shown that the choice of ligands is a key factor in achieving high operational characteristics. It has been shown that the photoconductivity sensitivity reaches 0.995 and the specific detectivity reaches 1.2×109 Jones when 1,2-ethadithiol is used as ligands.

PL intensity quenching and the PL lifetime reduction of fluorophores located close to graphene derivatives are generally explained by charge and energy transfer processes. Analyzing the PL from PbS QDs in rGO/QD systems, we observed a substantial reduction in average PL lifetimes with an increase in rGO content that cannot be interpreted solely by these two processes. To explain the PL lifetime dependence on the rGO/QD component ratio, we propose a model based on the Auger recombination of excitations involving excess holes left in the QDs after the charge transfer process. To validate the model, we conducted additional experiments involving the external engineering of free charge carriers, which confirmed the role of excess holes as the main QD PL quenching source. A mathematical simulation of the model demonstrated that the energy transfer between neighboring QDs must also be considered to explain the experimental data carefully. Together, Auger recombination and energy transfer simulation offers us an excellent fit for the average PL lifetime dependence on the component ratio of the rGO/QD system.

Hybrid nanomaterials based on graphene and PbS quantum dots (QDs) have demonstrated promising applications in optoelectronics. However, the formation of high-quality large-area hybrid films remains technologically challenging. Here, we demonstrate that ligand-assisted self-organization of covalently bonded PbS QDs and reduced graphene oxide (rGO) can be utilized for the formation of highly uniform monolayers. After the post-deposition ligand exchange, these films demonstrated high conductivity and photoresponse. The obtained films demonstrate a remarkable improvement in morphology and charge transport compared to those obtained by the spin-coating method. It is expected that these materials might find a range of applications in photovoltaics and optoelectronics.

Lead sulfide (PbS) quantum dots (QDs) have been covalently attached to reduced graphene oxide (rGO). Thin films from a hybrid rGO-PbS nanomaterial have been formed by a Langmuir-Blodgett technique. We found that oleic acid on QDs surface induces self-organization of high-quality rGO-PbS films with a thickness of 1-2 monolayer. To utilize these films in optoelectronic devices, post-deposition ligand exchange procedures have been applied. We found both high conductivity and light-sensitivity in EDT- and TBAI-treated rGO-PbS films. We have applied rGO-PbS hybrid films to enhance the performance of a hybrid and heterojunction QD-based solar cells.

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers.