Aabhash Shrestha

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 chalcogenides (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, and bio‐electronics. 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 properties of QDs is well understood for their applications in various devices. In this Review we elaborate 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 photovoltaic applications.

Quantenpunkte (QDs) von Bleichalkogeniden (z. B. PbS, PbSe und PbTe) sind nahinfrarotaktive Materialien, die großes Potenzial für einen breiten Bereich von Anwendungen wie Photovoltaik, Optoelektronik, Sensorik und Bioelektronik zeigen. Oberflächenliganden spielen eine wesentliche Rolle bei der Herstellung und postsynthetischen Modifizierung von QDs sowie bei deren Einsatz in Anwendungen. Daher ist ein gutes Verständnis des Einflusses von Oberflächenliganden auf die Synthese und Eigenschaften von QDs für deren Anwendungen in verschiedenen Bauelementen unerlässlich. Der vorliegende Aufsatz beschäftigt sich mit der Anwendung kolloidaler Synthesetechniken zur Herstellung von bleichalkogenidbasierten QDs. Der Schwerpunkt liegt auf dem Einfluss von Oberflächenliganden auf die QD‐Synthese sowie dem Ligandenaustausch in Lösung. Angesichts der Bedeutung von Bleichalkogenid‐QDs als möglichen Lichtsammlern richten wir unsere Aufmerksamkeit besonders auf die aktuellen Fortschritte von PV‐Anwendungen mit diesen QDs.

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_x) decorated nitrogen and sulfur co‐doped carbon nanotube heteroelectrocatalyst coated with FL‐BP (FL‐BP@N,S‐doped CNTs‐CoS_x) 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.

As an alternative to platinum (Pt), hybrid electrocatalysts based on sulfur‐doped graphene with FeS₂ microspheres (SGN‐FeS₂) were used as a counter electrode (CE) in dye‐sensitized solar cells (DSSCs). Benefiting from the high conductivity of SGN and excellent electrocatalytic activity of the FeS₂, the bifunctional hybrid electrocatalyst‐based device displays a power conversion efficiency (PCE) of 8.1%, which is comparable to that (8.3%) of traditional Pt CE‐based DSSC, while also exhibiting excellent stability in ambient conditions. These characteristics, in addition to its low‐cost and facile preparation, make the SGN–FeS₂ hybrid an ideal CE material for DSSCs.

The use of polydopamine as a nitrogen containing precursor to generate catalytically active nitrogen‐doped carbon (CN_x) materials on carbon nanotubes (CNTs) is reported. These N‐doped CN_x/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 CN_x/CNTs is investigated in detail. The best performing device fabricated with the CN_x/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 CN_x/CNTs materials show great potential to address the issues associated with the Pt electrocatalyst including the high cost and scarcity.

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.