Engineering of highly performing nanomaterials, capable of rapid detection of trace concentrations of gas molecules at room temperature, is key to the development of the next generation of miniaturized chemical sensors. Here, a highly performing nanoheterojunctions layout is presented for the rapid room‐temperature chemical sensing of volatile organic compounds down to ten particles per billion concentrations. The layout consists of a 3D network of nickel oxide–zinc oxide (NiO–ZnO) p–n semiconductors with grain size of ≈20 nm nanometers and a porosity of ≈98%. Notably, it is observed that the formation of the p–n heterojunctions by decoration of a ZnO nanoparticle networks with NiO increases the sensor response by more than four times while improving the lower limit of detection. Under solar light irradiation, the optimal NiO–ZnO nanoheterojunction networks demonstrate a strong and selective room‐temperature response to two important volatile organic compounds utilized for breath analysis, namely acetone and ethanol. Furthermore, these NiO–ZnO nanoheterojunctions show an inverse response to acetone from that observed for all others reducing gas molecules (i.e., ethanol, propane, and ethylbenzene). It is believed that these novel insights of the optoelectrochemical properties of ultraporous nanoheterojunction networks provide guidelines for the future design of low‐power solid‐state chemical sensors.
Quantum dots (QDs) of lead chacogenides (e.g. PbS, PbSe and PbTe) are attractive near-infrared (NIR) active materials that show great potential in a wide range of applications such as photovoltaics (PV), optoelectronics, sensors, bio-electronics and many others. The successful utilization of these functional materials requires deep understanding of their synthesis, properties and material modification process. The surface ligand plays an essential role in the production of QDs, post-synthesis modification and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and property of QDs is well understood for their applications in various devices. Present review elaborates the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in PV applications. This review concludes by providing some important research directions for the future use of lead chalcogenide QDs in solar cells.
The use of polydopamine as a nitrogen containing precursor to generate catalytically active nitrogen‐doped carbon (CNx) materials on carbon nanotubes (CNTs) is reported. These N‐doped CNx/CNT materials display excellent electrocatalytic activity toward the reduction of triiodide electrolyte in dye‐sensitized solar cells (DSSCs). Further, the influence of various synthesis parameters on the catalytic performance of CNx/CNTs is investigated in detail. The best performing device fabricated with the CNx/CNTs material delivers power conversion efficiency of 7.3%, which is comparable or slightly higher than that of Pt (7.1%) counter electrode‐based DSSC. These CNx/CNTs materials show great potential to address the issues associated with the Pt electrocatalyst including the high cost and scarcity.
Research into efficient synthesis, fundamental properties, and potential applications of phosphorene is currently the subject of intense investigation. Herein, solution-processed phosphorene or few-layer black phosphorus (FL-BP) sheets are prepared using a microwave exfoliation method and used in photoelectrochemical cells. Based on experimental and theoretical (DFT) studies, the FL-BP sheets are found to act as catalytically active sites and show excellent electrocatalytic activity for triiodide reduction in dye-sensitized solar cells. Importantly, the device fabricated based on the newly designed cobalt sulfide (CoS ) decorated nitrogen and sulfur co-doped carbon nanotube heteroelectrocatalyst coated with FL-BP (FL-BP@N,S-doped CNTs-CoS ) displayed an impressive photovoltaic efficiency of 8.31 %, outperforming expensive platinum based cells. This work paves the way for using phosphorene-based electrocatalysts for next-generation energy-storage systems.
Transparent conductive oxides (TCOs) are highly desirable for numerous applications ranging from photovoltaics to light-emitting diodes and photoelectrochemical devices. Despite progress, it remains challenging to fabricate porous TCOs (pTCOs) that may provide, for instance, a hierarchical nanostructured morphology for the separation of photoexcited hole/electron couples. Here, we present a facile process for the fabrication of porous architectures of aluminum-doped zinc oxide (AZO), a low-cost and earth-abundant transparent conductive oxide. Three-dimensional nanostructured films of AZO with tunable porosities from 10 to 98% were rapidly self-assembled from flame-made nanoparticle aerosols. Successful Al doping was confirmed by X-ray photoemission spectroscopy, high-resolution transmission electron microscopy, elemental mapping, X-ray diffraction, and Fourier transform infrared spectroscopy. An optimal Al-doping level of 1% was found to induce the highest material conductivity, while a higher amount led to partial segregation and formation of aluminum oxide domains. A controllable semiconducting to conducting behavior with a resistivity change of more than 4 orders of magnitudes from about 3 × 102 to 9.4 × 106 Ω cm was observed by increasing the AZO film porosity from 10 to 98%. While the denser AZO morphologies may find immediate application as transparent electrodes, we demonstrate that the ultraporous semiconducting layers have potential as a light-driven gas sensor, showing a high response of 1.92–1 ppm of ethanol at room temperature. We believe that these tunable porous transparent conductive oxides and their scalable fabrication method may provide a highly performing material for future optoelectronic devices.
The quantum dots (QDs) of lead sulphide (PbS) are attractive near-infrared (NIR) active materials and have promising applications in a wide variety of applications. Till date many efforts have been made on optimizing its synthesis; however, current mechanistic understanding involving the nucleation and growth of these QDs has not reached the same level as that for other QDs. In this study, we present a detailed understanding on synthesis mechanism of PbS QDs so as to provide guidance for future QDs synthesis. The synthesis of PbS QDs is largely independent of classical nucleation process and the hot-injection of precursors may not be necessary for the successful synthesis of PbS QDs. The synthesis is basically a growth dominated process and is controlled by the Ostwald ripening of PbS QDs. In addition, reaction temperature and ligand are the key parameters for controlling QD growth. Temperature provides energy for overcoming activation barrier of QD growth while the ligands enhance QD growth via altering the environment for QD growth. Following the mechanism governing the synthesis of PbS QDs, we demonstrate that the size tuning of PbS QDs in ultra-small (<2 nm) can be achieved, which has been typically challenging following the hot injection synthesis.
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Colloidal quantum dot (QD) nanocrystals of lead sulfide (PbS) have promising applications in diverses cientific fields due to their size-tuned band gaps, but the batch synthesis of differently sized QDs is cumbersome. In this paper,w er eport ar obust methodt os ynthesize monodisperse PbS QDs through an ovel "living" growth process, in which as eries of differently sized QDs can be easily produced upon step-wise heating the preformed seed QDs in the presence of excessive PbS monomers, that is, un-crystallized PbS. The mechanism for such aQ D growth is associated with the combination of "living" monomer addition to existing QDs to increase particles izes and Ostwald ripening to focus particles. The outcomei s not only able to produce various high-qualityQDs without extensive synthetic work, but also provide new insight into the mechanismo fs ynthesizings emiconducting colloidal nanocrystals.Ever since the recognition that the quantum confinement effect determines the optical properties of cadmium sulfide (CdS) nanocrystals, [1] there have been tremendous efforts on the synthesis of various types of semiconducting nanocrystals. [2] Among them,c olloidal near-infrared( NIR) quantum dots (QDs) have received growing interest due to their size tunability across the NIR region relevant to applications in bioimaging [3] (700-1000 nm), telecommunications [2c] (1300-1600 nm), photovoltaics, [4] and many others. Among them, lead sulfide (PbS) QDs have attractedg reat attention due to their high molar extinction coefficients, [5] large excitonic Bohr radii ( % 18 nm), [3a, 5a, c] multiple exciton generation, [6] and better air stabilityr elative to other lead-based chalcogenides. [7] To date, many efforts have been reported on optimizing the synthesis of PbS QDs, such as using various chemical precursors, [2c, 5a, 8] different stabilizingl igands, [5a, 9] diverse synthesis media, [7,8,10] and miscellaneous methodologies. [2c, 7, 11] However,i ta lways requires extensive synthetic work to produce differently sized colloidal nanoparticles. Generally,t here are two approaches to tune the particles izes of QDs:m anipulatings ynthetic precursor ratios and controlling synthesis temperatures. The variation in synthetic precursor ratios requires multiple batches to produce differently sized nanoparticles, [2c, 5a] whereas controlling the synthesis temperature is sensitive to small variations in precursor types andr atios. [11a, 12] The shift of excitonic wavelength in the absorption spectrum of PbS QDs during as ingle batch synthesis can be varied between 100 to 450 nm by changing precursor ratios or synthesis temperatures. [11a, 12] The batch-to-batch variation cannot be avoided. Moreover,t hese synthesis procedures are complicated duet ot he lacko ffundamental understanding of the precursor conversion kinetics [13] (whichv aries with differentp recursors and ligands), nucleation, and crystal-growthm echanisms. [14] In this study,w er eport ar obusts trategy to synthesize differently sized PbS QDs by step-by-step heati...
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