Se Precursor Research Articles

Precursor Reactivity‐Controlled Synthesis of ZnSeTe Spherical Quantum Wells with Narrow and Symmetric Photoluminescence

AbstractEnvironment‐friendly ZnSeTe quantum dots (QDs) are considered as potential blue light emitters. However, due to the large reaction activity difference between Se and Te precursors, ZnSeTe QDs usually can not uniformly alloyed and generate lattice distortion, reducing the color purity or photoluminescence quantum yield (PLQY). A ZnSe/ZnSeTe/ZnSe spherical quantum well (SQW) structure with quasi type‐II energy band arrangement is designed. To promote the uniform growth and even alloying of ternary ZnSeTe, weakly active biphenyltellurium (Ph2Te2) is applied as a new Te source for balancing the reactivity between Te and Se. Epitaxial growth of high crystallinity ZnSeTe with greatly reduced defects is obtained. After ZnS outer layer passivation, the obtained ZnSe/ZnSeTe/ZnSe/ZnS QDs exhibit a high PLQY (≈84%) and a narrow full width at half maxima (19 nm) without asymmetric broaden at 455 nm, contributing to an ultrahigh color purity, which is among the best photoluminescence performance for blue emitting ZnSeTe based QDs. This work provides a new balance strategy of precursor reactivity for synthesizing high color purity and heavy metal free blue ZnSeTe QDs.

A novel Se-diffused selenization strategy to suppress bulk and interfacial defects in Sb2Se3 thin film solar cell

In recent years, vacuum-based deposition of antimony selenide (Sb2Se3) thin films has garnered significant attention owing to its easy and impurity-free fabrication, along with exceptional power conversion efficiency (PCE). However, the necessary post-selenization process comes with a shortcoming of instigating buried Sb2Se3/molybdenum (Mo) back-contact interface defects. This study introduces a novel Se-diffusion post-selenization technique to precisely regulate the selenium reaction atmosphere, preventing void formation on the Sb2Se3 thin film surface and maintaining film quality for enhanced device efficiency. An optimized selenization condition with a precise Se precursor film thickness led to obtaining highly crystalline, preferentially (hk1) oriented, and large-grained Sb2Se3 films. Furthermore, a meticulous Se diffusion in Sb2Se3 film reduced the inevitable MoSe2 layer thickness at the Mo surface, thereby enhancing the quality of the back contact interface. The Sb2Se3 solar cell that was selenized to optimal level showed significant enhancements, raising the fill factor from 40.06 % to 45.12 % and improving the device efficiency from 2.89 % to 3.57 %. Our newly developed selenization strategy establishes a successful approach to regulate the Sb2Se3 film quality by addressing a crucial challenge in improving the efficiency of antimony chalcogenide solar cells.

One-pot synthesis of NiFe foam-supported FeWO4/Ni3Se2 nanocomposites and their enhanced electrocatalytic performance for oxygen evolution reaction

The development of composite nanocatalysts having strong interactions with electrode materials is important to enhance the reactivity and stability of catalysts used in electrochemical reactions. In this study, we report a method for directly growing FeWO4/Ni3Se2 composite nanocatalysts on the nickel–iron foam (NFF) surfaces, utilizing nickel (Ni) and iron (Fe) in NFF as precursors for synthesizing Ni3Se2 and FeWO4, respectively. The composite nanocatalysts, serving as electrode materials, are formed by the reaction of W precursor and Se precursors with NFF and exhibited high catalytic activity and long-term stability in oxygen and hydrogen evolution reactions.

Organoborane Se and Te Precursors for Controlled Modulation of Reactivity in Nanomaterial Synthesis.

To exploit the distinctive optoelectrical properties of nanomaterials, precise control over the size, morphology, and interface structure is essential. Achieving a controlled synthesis demands precursors with tailored reactivity and optimal reaction temperatures. Here, we introduce organoborane-based selenium and tellurium precursors borabicyclononane-selenol (BBN-SeH) and tellurol (BBN-TeH). The reactivity of these precursors can be modified by commercially available additives, covering a wide range of intermediate reactivity and filling significant reactivity gaps in existing options. By allowing systematic adjustment of growth conditions, they achieve the controlled growth of quantum dots of various sizes and materials. Operating via a surface-assisted conversion mechanism, these precursors rely on surface coordination for activation and undergo quantitative deposition on coordinating surfaces. These properties allow precise control over the radial distribution and density of different chalcogenide atoms within the nanoparticles. Diborabicyclononanyl selane ((BBN)2Se), an intermediate from the BBN-SeH synthesis, can also serve as a selenium precursor. While BBN-SeH suppresses nucleation, (BBN)2Se exhibits efficient nucleation under specific conditions. By leveraging these distinct activation behaviors, we achieved a controlled synthesis of thermally stable nanoplates with different thicknesses. This study not only bridges critical reactivity gaps but also provides a systematic methodology for precise nanomaterial synthesis.

Aqueous synthesis of highly luminescent AgInSe2/ZnS core/shell nanocrystals

Ternary I-III-VI chalcopyrite-type nanocrystals (NCs) range among the most important alternative materials to Cd-based NCs. Within this materials family, AgInSe2 (AISe) presents a narrower bandgap than widely studied AgInS2 (AIS), making it more suitable for numerous applications. At present, it remains a long-standing challenge to directly synthesize high-quality AISe core and AISe/ZnS core/shell NCs in aqueous solution at atmospheric pressure. In this work, we describe their synthesis using glutathione and citric acid as dual stabilizers. First, to form AISe core NCs, the Se precursor is injected into a solution containing the Ag and In complexes at 96 °C for 20 min. In the second step, the AISe/ZnS core/shell structure is created by growing the ZnS shell on the AISe NCs surface at 90 °C for 60 min. The synthesized AISe and AISe/ZnS core/shell NCs are characterized using X-ray diffraction, transmission electron microscopy, and UV-Vis absorption and photoluminescence for optical spectroscopies. After the growth of the ZnS shell, AISe/ZnS core/shell NCs exhibit higher photostability and emit intense luminescence at a wavelength of 680 nm with an impressive quantum yield (QY) of 30 %, which represents a threefold higher than the AISe core NCs. These properties make the aqueous soluble AISe/ZnS core/shell NCs favorable candidates for lighting, displays, and biological imaging applications.

Effect of substrate temperature on structure, morphology and optical properties of Sb2Se3 thin films fabricated by chemical-molecular beam deposition method from Sb and Se precursors for solar cells

Sb2Se3 thin films were obtained by chemical-molecular beam deposition on soda-lime glass from high purity Sb and Se precursors at 400 °C, 450 °C and 500 °C substrate temperature. Due to the precise control of the Sb/Se ratio, Sb2Se3 thin films with stoichiometric composition were obtained, which was confirmed by energy-dispersive X-ray microanalysis. The effect of substrate temperature on morphology, structure and optical properties of Sb2Se3 thin-films were studied by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy and from the analysis of absorption and transmission spectra of the films. Average diameters and lengths of Sb2Se3 rods deposited at different substrate temperature were the range of 0.5–2 µm and 1–4 µm respectively which was grown at different slope and compactness to the substrate. The optical bandgap of the films was determined from the transmission and reflection spectra and 1.16, 1.21 and 1.26 eV band gap energies were observed for 500, 450 and 400 ℃ substrate temperature Sb2Se3 thin films respectively.

Solution-processed Sb2Se3 photocathodes under Se-rich conditions and their photoelectrochemical properties.

In this study, selenium (Se)-rich antimony selenide (Sb2Se3) films were fabricated by applying a solution process with the solvents ethylenediamine and 2-mercaptoethanol to optimize the photoelectrochemical (PEC) performance of the Sb2Se3 photocathode. Various antimony (Sb)-Se precursor solutions with different molar ratios of Sb and Se (Sb : Se = 1 : 1.5, 1 : 3, 1 : 4.5, 1 : 7.5, and 1 : 9) were prepared to attain Se-rich fabrication conditions. As a result, the Se-rich Sb2Se3 films fabricated using the Sb-Se precursor solution with a molar ratio of Sb : Se = 1 : 7.5 exhibited an improved PEC performance, compared to the stoichiometric Sb2Se3 film. The charge transport was improved by the abundant Se element and thin selenium oxide (Se2O3) layer in the Se-rich Sb2Se3 film, resulting in a decrease in Se vacancies and substitutional defects. Moreover, the light utilization in the long wavelength region above 800 nm was enhanced by the light-trapping effect because of the nanowire structure in the Se-rich Sb2Se3 film. Hence, the optimal Se-rich Sb2Se3 photocathodes showed an improved photocurrent density of -0.24 mA cm-2 at the hydrogen evolution reaction potential that was three times higher than that of the stoichiometric Sb2Se3 photocathodes (-0.08 mA cm-2).

Atomic Layer Deposition and Characterization of Bi1Se1 Thin Films

Van der Waals (vdWs) heterostructured materials have attracted considerable interest due to their intriguing physical properties. Here, we report on the deposition of BiSe by atomic layer deposition (ALD) using Bi(NMe2)3 and Se(SnMe3)2 as volatile and reactive Bi and Se precursors, respectively. The growth rate varies from 1.5 to 2.0 Å/cycle in the deposition temperature range of 90–120 °C. Higher deposition temperatures lead to increased grain sizes and enhanced crystallinity of resulting films. Further microstructure characterization reveals the formation of crystalline domains with varying orientations and nanotwinned boundaries. The presence of Bi-Bi zigzag bilayers and the formation of the BiSe phase were confirmed by the existence of the Bi-Bi binding energy peak in the XPS spectra and Raman spectra. Furthermore, the electrical conductivity of BiSe ranged from 1420 to 1520 S/cm due to the ultrahigh carrier concentration (2–3.5 × 1021 cm−3), which is the highest among undoped bismuth selenide-based materials.

Acid selenites as new selenium precursor for CdSe quantum dot synthesis

Chemical precursors for nanomaterials synthesis have become essential to tune particle size, composition, morphology, and unique properties. New inexpensive precursors investigation that precisely controls these characteristics is highly relevant. We studied new Se precursors, the acid selenites (R–O–SeOOH), to synthesize CdSe quantum dots (QDs). They were produced at room temperature by the ▪ reaction with alcohols having different alkyl chains and were characterized by 1H NMR confirming their structures. This unprecedented precursor generates high-quality CdSe nanocrystals with narrow size distribution in the zinc-blend structure showing controlled optical properties. Advanced characterization detailed the CdSe structure showing stacking fault defects and its dependence on the used R–O–SeOOH. The QDs formation was examined using a time-dependent growth kinetics model. Differences in the nanoparticle surface structure influenced the optical properties, and they were correlated to the Se-precursor nature. Small alkyl chain acid selenites generally lead to more controlled QDs morphology, while the bigger alkyl chain leads to slightly upper quantum yields. Acid selenites can potentially replace Se-precursors at competitive costs in the metallic chalcogenide nanoparticles. ▪ is chemically stable, and alcohols are cheap and less toxic than the reactants used today, making acid selenites a more sustainable Se precursor.

Improved CZTSe solar cell efficiency via silver and germanium alloying

In this study, we report systematic investigation of the effects of Ag and Ge alloying on properties of CZTSe layers, as well as, on the performance of solar cells fabricated using these films. In this context, Ag-Ge doped CZTSe layers were produced by selenization of Cu/Sn/Zn/Cu/(Ag,Ge)/Se precursor stack structures using rapid thermal processing. All precursor stacks and the Ag-Ge doped CZTSe films obtained after selenization exhibited (Cu + Ag)-poor and Zn-rich chemical composition. XRD studies demonstrated pure kesterite phase for all reacted films. Raman spectra confirmed this finding. Cross-sectional SEMs showed large grain structure, which resulted from Ag-Se and Ge-Se liquid phase formation that assisted crystal growth during high temperature annealing. While a slight Ag-front-gradient was achieved in Ag-doped CZTSe film, the Ag gradient disappeared with incorporation of Ge into the lattice. Addition of Ge formed a gradient within the material such that near-contact region was more Ge-rich. Solar cells fabricated using films with various compositions demonstrated that double doping CZTSe with both Ag and Ge improved the device efficiency from about 5 % to over 8 %.

2H-2M Phase Control of WSe2 Nanosheets by Se Enrichment Toward Enhanced Electrocatalytic Hydrogen Evolution Reaction.

The phase control of transition metal dichalcogenides (TMDs) is an intriguing approach for tuning the electronic structure toward extensive applications. In this study, WSe2 nanosheets synthesized via a colloidal reaction exhibit a phase conversion from semiconducting 2H to metallic 2M under Se-rich growth conditions (i.e., increasing the concentration of Se precursor or lowering the growth temperature). High-resolution scanning transmission electron microscopy images are used to identify the stacking sequence of the 2M phase, which is distinctive from that of the 1T' phase. First-principles calculations employing various Se-rich models (intercalation and substitution) indicated that Se enrichment induces conversion to the 2M phase. The 2M phase WSe2 nanosheets with the Se excess exhibited enhanced electrocatalytic performance in the hydrogen evolution reaction (HER). In situ X-ray absorption fine structure studies suggested that the excess Se atoms in the 2M phase WSe2 enhanced the HER catalytic activity, which is supported by the Gibbs free energy (ΔGH* ) of H adsorption and the Fermi abundance function. These results provide an appealing strategy for phase control of TMD catalysts.

Revealing Two Distinct Formation Pathways of 2D Wurtzite‐CdSe Nanocrystals Using In Situ X‐Ray Scattering

AbstractUnderstanding the mechanism underlying the formation of quantum‐sized semiconductor nanocrystals is crucial for controlling their synthesis for a wide array of applications. However, most studies of 2D CdSe nanocrystals have relied predominantly on ex situ analyses, obscuring key intermediate stages and raising fundamental questions regarding their lateral shapes. Herein, the formation pathways of two distinct quantum‐sized 2D wurtzite‐CdSe nanocrystals — nanoribbons and nanosheets — by employing a comprehensive approach, combining in situ small‐angle X‐ray scattering techniques with various ex situ characterization methods is studied. Although both nanostructures share the same thickness of ≈1.4 nm, they display contrasting lateral dimensions. The findings reveal the pivotal role of Se precursor reactivity in determining two distinct synthesis pathways. Specifically, highly reactive precursors promote the formation of the nanocluster‐lamellar assemblies, leading to the synthesis of 2D nanoribbons with elongated shapes. In contrast, mild precursors produce nanosheets from a tiny seed of 2D nuclei, and the lateral growth is regulated by chloride ions, rather than relying on nanocluster‐lamellar assemblies or Cd(halide)2–alkylamine templates, resulting in 2D nanocrystals with relatively shorter lengths. These findings significantly advance the understanding of the growth mechanism governing quantum‐sized 2D semiconductor nanocrystals and offer valuable guidelines for their rational synthesis.

Fe species-decorated nickel selenides on Ni foam (FNS/NF) for efficient overall water splitting

For industrial-scale green hydrogen production by water electrolysis, the catalyst used should exhibit the following characteristics: low cost, ease of use, high electrochemical activity, and good stability. In this study, we prepare a Pt replacement catalyst that can be used as an effective catalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) as well as exhibits excellent stability. FeOOH-decorated nickel selenide on a Ni foam (FNS/NF), synthesized by decorating FeOOH on a NiSe/NF prepared by reacting an NF with a Se precursor under a hydrothermal condition, exhibited superior electrocatalytic activities in OER and HER. Furthermore, the (FNS/NF-5)||(FNS/NF-5) full-cell requires only 1.599 V to obtain 10 mA cm−2, demonstrating the utmost overall water splitting performance with convenience in a simple cell configuration.

Acid-Resistant Near-Infrared II Ag2Se Quantum Dots for Gastrointestinal Imaging.

With the development of near-infrared II (NIR-II) fluorescence imaging, Ag2Se quantum dots (QDs) have become promising label candidates due to their negligible toxicity and narrow band gap. Despite their potential for gastrointestinal (GI) imaging, the application of Ag2Se QDs still presents significant challenges due to issues such as fluorescence extinction or poor stability in the complex digestive microenvironment. Herein, we have proposed a novel approach to the continuous production of Se precursors using glutathione (GSH) as the reductant under acidic conditions, realizing the continuous growth of water-dispersible Ag2Se QDs. The Ag2Se QDs emitting at 600-1100 nm have been successfully synthesized. Meanwhile, the silver-rich surface of the synthesized NIR-II Ag2Se QDs has been passivated well with the dense GSH, resulting in exceptional colloidal stability and photostability and endowing them with acid resistance. As a result, the obtained NIR-II Ag2Se QDs have exhibited remarkable stability in gastric acid, thus enabling their utilization for long-term real-time monitoring of GI peristalsis via NIR-II fluorescence imaging. Moreover, in contrast to conventional barium meal-based X-ray imaging, NIR-II fluorescence imaging with as-prepared NIR-II Ag2Se QDs can offer clearer visualization of fine intestinal structures, with a width as small as 1.07 mm. The developed strategy has offered a new opportunity for the synthesis of acid-resistant nanocrystals, and the acid-resistant, low-toxicity, and biocompatible NIR-II Ag2Se QDs synthesized in this work show a great promise for GI imaging and diagnosis of GI diseases in vivo.

Make Selenium Reactive Again: Activating Elemental Selenium for Synthesis of Metal Selenides Ranging from Nanocrystals to Large Single Crystals.

The inertness of elemental selenium is a significant obstacle in the synthesis of selenium-containing materials at low reaction temperatures. Over the years, several recipes have been developed to overcome this hurdle; however, most of the methods are associated with the use of highly toxic, expensive, and environmentally harmful reagents. As such, there is an increasing demand for the design of cheap, stable, and nontoxic reactive selenium precursors usable in the low-temperature synthesis of transition metal selenides with vast applications in nanotechnology, thermoelectrics, and superconductors. Herein, a novel synthetic route has been developed for activating elemental selenium by using a solvothermal approach. By comprehensive 77Se NMR, Raman, and infrared spectroscopies and gas chromatography-mass spectrometry, we show that the activated Se solution contained HSe-, [Se-Se]2-, and Se2- ions, as well as dialkyl selenide (R2Se) and dialkyl diselenide (R-Se-Se-R) species in dynamic equilibrium. This also corresponded to the first observation of naked Se22- in solution. The versatility of the developed Se precursor was demonstrated by the successful synthesis of (i) the polycrystalline room-temperature modification of the β-Ag2Se thermoelectric material; (ii) large single crystals of superconducting β-FeSe; (iii) CdSe nanocrystals with different particle sizes (3-10 nm); (iv) nanosheets of PtSe2; and (v) mono- and dibenzyl selenides and diselenides at room temperature. The simplicity and diversity of the developed Se activation method holds promise for applied and fundamental research.

Nanostructured PbSe Films Deposited by Spray Pyrolysis Using PbSe Colloidal Solutions.

This work describes the spray pyrolysis deposition of PbSe films, using as-prepared PbSe colloids as the starting solution. The PbSe colloids were prepared by using the alkahest approach, where Pb and Se precursors were made to react with the following green polyols: glycerin, ethylene glycol, and propylene glycol, to subsequently spray them onto glass substrates. The results of the characterization indicated that amine or thiol groups-free and single-phase rock-salt cubic PbSe powder was obtained, producing nanocrystals 16-30 nm in size. X-ray diffraction also showed that the PbSe films containing PbSeO3 and PbO·xH2O as impurity phases were produced during the deposition. The morphology of the powders and films was developed by a self-assembly process, in which the primary PbSe nanoparticles self-assemble to produce peanut-like microstructures. Additionally, a non-continuous and porous feature was formed in the thick films. Certain films revealed optical structures characterized by broad- and low-intensity bands resembling an exciton-like behavior. This could be attributed to the presence of nanocrystals with a size less than the Bohr radius, indicating reminiscent quantum effects. The results suggest that the usage of colloidal dispersions as spray solutions represents an effective approach to forming PbSe films, as well as that the synthesis method allows for the elimination of thiol and amine groups before deposition, significantly simplifying the process.

Understanding the growth mechanisms of ultrasmall silver selenide quantum dots for short-wave infrared detectors

Colloidal quantum dots (CQDs) allow for wavelength-tunable, economic, and elegant access to the infrared (IR) spectrum by utilizing inter- and intraband excitonic transitions in narrow bandgap semiconductors. With the emergence of new applications for IR detection, developing competitive non-toxic and environmentally benign alternatives to heavy metal-containing semiconductors is of increasing importance. Over the last decade, silver selenide (Ag2Se) has emerged as an alternative to lead- and mercury-based QDs, especially with large, intraband Ag2Se CQDs showing promising performance in the mid-wave IR. Herein we explored the critical nucleation and growth mechanisms of ultrasmall (2.5–3.5 nm) interband absorbing Ag2Se CQDs operating in the near to short-wave IR. Classical nucleation and growth was observed at most reaction conditions, with a growth temperature of 140 °C and a Ag:Se precursor molar ratio of 1:2 providing the most robust control over the IR absorption spectrum. We proceeded to perform an in-depth study of the impact of surface ligand chemistry of CQD thin-films on resulting optoelectronic properties. By tuning the functional groups and optimizing ligand exchange parameters, we obtained IR responsivity values of ∼25 mA/W in photoconductor devices and ∼1.8 mA/W in photodiode devices in the range 800 – 1250 nm.

High-performance Ag2Se film by a template method for flexible thermoelectric generator

Herein, we developed a facile method to prepare a high-performance Ag2Se thermoelectric (TE) film. First, Ag2Se powders were synthesized by the reaction between Ag nanowires (NWs) with Se precursor at room temperature (RT), then vacuum filtered on a nylon membrane, and finally hot pressed. The film exhibits a high power factor of 1636.9 μW m−1 K−2 at RT via optimizing the Ag/Se ratio. The film exhibits good flexibility because of the nylon substrate and the nylon well combined with the Ag2Se film. Moreover, a flexible TE generator (f-TEG) consisting of six optimized film legs was assembled, and it generates a maximum output power of ∼3.42 μW (corresponding power density of ∼13.5 W m−2) under a temperature gradient of 31.4 K. This work paves a simple, fast, and feasible route to prepare high-performance flexible Ag2Se film.

Improved stability and luminescent efficiency of AgInSe2 nanocrystals by shelling with ZnS

In this paper, AgInSe2 (AISe) core and AgInSe2/ZnS (AISe/ZnS) core/shell nanocrystals (NCs) were synthesised by a one-pot method in an organic solvent. Firstly, the synthesis of AIS core NCs with different sizes was performed by hot-injection of Se precursor into the Ag and In complexes at different temperatures from 100 °C to 180 °C for a reaction time of 20 min Then, the ZnS was grown on the surface of AISe NCs at 150 °C for 60 min to produce the AISe/ZnS core/shell structures. The as-synthesised AISe core and AISe/ZnS core/shell NCs were characterised by using x-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and optical spectroscopies (UV–vis absorption and photoluminescence (PL)). After shelling ZnS layer, AISe/ZnS core/shell NCs become more stable (12 months) in ambient air and emit strong luminescence with a high quantum yield (QY) of 40% in the range from 610 nm to 762 nm by varying the reaction temperature of AISe core synthesis from 100 °C to 180 °C. The observed increase of QY and blue-shift in photoluminescence spectra after coating ZnS on surface AISe core NCs are rationalised by the formation of the alloyed structure and passivation of surface states. With their outstanding luminescent properties, AISe core and AISe/ZnS core/shell NCs are very promising in designing emitters for solid-state lighting sources in the greenhouse and in-door farming and bio-related devices.

Effects of hydrothermal synthesis conditions on material properties of Cu-Se compounds for thermoelectric and photothermal energy conversion

Copper selenide (CuSe) is a promising material for these applications due to its unique properties such as meaningful electrical conductivity, Seebeck coefficient, and photothermal conversion efficiency. Here, a systematic investigation into the hydrothermal synthesis and characterization of copper selenides (CuSe) was performed for thermoelectric and photothermal applications. Depending on the feeding ratio of the Cu and Se precursors and reducing agent, CuSe2, CuSe, and Cu2Se were synthesized at a relatively low temperature and within a limited time frame. The crystal growth and morphology of the compounds were composition-dependent, which led to variations in their electrical conductivity, Seebeck coefficient, and thermoelectric properties. Synthesized Cu-Se compounds also showed promising photothermal conversion characteristics, which were utilized to increase the energy harvesting of the thermoelectric module under light exposure. This study provide important insights into the relationship between the synthesis conditions and the material properties, as well as the potential of CuSe-based materials for thermoelectric and photothermal applications.