Selective Oxidizing Gas Sensing and Dominant Sensing Mechanism of <i>n</i>‑CaO-Decorated <i>n</i>‑ZnO Nanorod Sensors

In this work, we investigated the NO₂ and CO sensing properties of <i>n</i>-CaO-decorated <i>n</i>-ZnO nanorods and the dominant sensing mechanism in <i>n</i>–<i>n</i> heterostructured one-dimensional (1D) nanostructured multinetworked chemiresistive gas sensors utilizing the nanorods. The CaO-decorated <i>n</i>-ZnO nanorods showed stronger response to NO₂ than most other ZnO-based nanostructures, including the pristine ZnO nanorods. Many researchers have attributed the enhanced sensing performance of heterostructured sensors to the modulation of the conduction channel width or surface depletion layer width. However, the modulation of the conduction channel width is not the true cause of the enhanced sensing performance of <i>n</i>–<i>n</i> heterostructured 1D gas sensors, because the radial modulation of the conduction channel width is not intensified in these sensors. In this work, we demonstrate that the enhanced performance of the <i>n</i>-CaO-decorated <i>n</i>-ZnO nanorod sensor is mainly due to a combination of the enhanced modulation of the potential barrier height at the <i>n</i>–<i>n</i> heterojunctions, the larger surface-area-to-volume ratio and the increased surface defect density of the decorated ZnO nanorods, not the enhanced modulation of the conduction channel width

Highly Sensitive Ratiometric Fluorescent Chemosensor for Silver Ion and Silver Nanoparticles in Aqueous Solution

A pyrene derivative chemosensor (<b>Pyr-WH</b>) based on a dipeptide shows a highly sensitive ratiometric response to Ag(I) as well as silver nanoparticles in aqueous solution at physiological pH. <b>Pyr-WH</b> penetrated live HeLa cells and exhibits a ratiometric response to intracellular Ag(I). The binding mode of <b>Pyr-WH</b> with Ag(I) was characterized based on fluorescence changes in different pH, NMR, and ESI mass spectrometer experiments

Silicotungstate, a Potential Electron Transporting Layer for Low-Temperature Perovskite Solar Cells

Thin films of a heteropolytungstate, lithium silicotungstate (Li₄SiW₁₂O₄₀, termed Li-ST), prepared by a solution process at low temperature, were successfully applied as electron transporting layer (ETL) of planar-type perovskite solar cells (PSCs). Dense and uniform Li-ST films were prepared on FTO glass by depositing a thin Li-ST buffer layer, followed by coating of a main Li-ST layer. The film thickness was controlled by varying the number of coating cycles, consisting of spin-coating and thermal treatment at 150 °C. In particular, by employing 60 nm-thick Li-ST layer obtained by two cycles of coating, the fabricated CH₃NH₃PbI₃ PSC device demonstrates the photovoltaic conversion efficiency (PCE) of 14.26% with <i>J</i>_SC of 22.16 mA cm^–2, <i>V</i>_OC of 0.993 mV and FF of 64.81%. The obtained PCE is significantly higher than that of the PSC employing a TiO₂ layer processed at the same temperature (PCE = 12.27%). Spectroscopic analyses by time-resolved photoluminescence and pulsed light-induced transient measurement of photocurrent indicate that the Li-ST layer collects electrons from CH₃NH₃PbI₃ more efficiently and also exhibits longer electron lifetime than the TiO₂ layer thermally treated at 150 °C. Thus, Li-ST is considered to be a promising ETL material that can be applied for the fabrication of flexible PSC devices

Novel Carbazole-Based Hole-Transporting Materials with Star-Shaped Chemical Structures for Perovskite-Sensitized Solar Cells

Novel carbazole-based hole-transporting materials (HTMs), including extended π-conjugated central core units such as 1,4-phenyl, 4,4′-biphenyl, or 1,3,5-trisphenylbenzene for promoting effective π–π stacking as well as the hexyloxy flexible group for enhancing solubility in organic solvent, have been synthesized as HTM of perovskite-sensitized solar cells. A HTM with 1,3,5-trisphenylbenzene core, coded as <b>SGT-411,</b> exhibited the highest charge conductivity caused by its intrinsic property to form crystallized structure. The perovskite-sensitized solar cells with <b>SGT-411</b> exhibited the highest PCE of 13.00%, which is 94% of that of the device derived from <i>spiro</i>-OMeTAD (13.76%). Time-resolved photoluminescence spectra indicate that <b>SGT-411</b> shows the shortest decay time constant, which is in agreement with the trends of conductivity data, indicating it having fastest charge regeneration. In this regard, a carbazole-based HTM with star-shaped chemical structure is considered to be a promising candidate HTM