Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics.
When the size of a material is reduced to the nanoscale, at or below the characteristic length scale that determines their properties, the material acquires completely new properties. On this length, its properties become sensitive to further changes in size, shape or whether they are hollow or solid. In this perspective article, we first discuss the different experimental techniques used in the synthesis, assembly and handling of colloidal solid or hollow nanoparticles with single and double shells. This is then followed by comparing the experimental and theoretical (DDA and FDTD) results for solid and hollow plasmonic nanoparticles as sensors using two different methods. The first method compares the plasmonic enhancement of the radiative properties of molecules or materials (e.g. in surface enhanced Raman scattering, SERS). The second one is based on the amount of the plasmon peak wavelength shift of the nanoparticle in media with different dielectric functions. In the last section of the perspective, we present a summary of the difference between the solid and hollow nanoparticles in nanocatalysis.We present the results of a number of experiments showing that the superior catalytic properties of hollow nanoparticles are due to catalysis occurring within the cavity of the hollow nanoparticles. Finally, using a femtosecond optical technique, we show that adding a second shell of a stiff metal (like Pt or Pd) to the plasmonic hollow nanoparticles increases their mechanical stability.
Conventional squaraine dyes exhibit an intense absorption band in the red region of the solar spectrum and with appropriate design can also have high energy absorption as well, making them interesting building blocks toward achieving panchromatic dyes for dye sensitized solar cell (DSSC) applications. In this report, eight squaraine dyes with thiophene, 4-hexyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole, dithieno[3,2-b:2′,3′-d]thiophene, and 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene (DTS) π-bridges with cyanoacetic acid (CA) and cyanophosphonic acid (PA) acceptor/anchoring groups are synthesized to extend the squaraine absorption into the 450–550 nm region and to provide different spatial arrangements of solubilizing groups. Squaraines with CA anchoring groups have higher power conversion efficiencies compared to their PA analogs, with the highest being 8.9% for the DTS-based dye, which is among the highest reported in the literature for squaraine dyes. This is due to high short circuit currents (J SC) and increased open circuit voltages (V OC). Dyes with PA anchoring groups exhibited lower J SC resulting from decreased charge injection efficiency, as determined by femtosecond transient absorption spectroscopy. This study suggests that out-of-plane bulky substituents may increase DSSC performance not only by increasing J SC through decreased aggregation but also by increasing V OC through decreased TiO2/electrolyte recombination.
Biological warfare agents are the most problematic of the weapons of mass destruction and terror. Both civilian and military sources predict that over the next decade the threat from proliferation of these agents will increase significantly. In this review we summarize the state of the art in detection and identification of biological threat agents based on PCR technology with emphasis on the new technology of microarrays. The advantages and limitations of real-time PCR technology and a review of the literature as it applies to pathogen and virus detection are presented. The paper covers a number of issues related to the challenges facing biological threat agent detection technologies and identifies critical components that must be overcome for the emergence of reliable PCR-based DNA technologies as bioterrorism countermeasures and for environmental applications. The review evaluates various system components developed for an integrated DNA microchip and the potential applications of the next generation of fully automated DNA analyzers with integrated sample preparation and biosensing elements. The article also reviews promising devices and technologies that are near to being, or have been, commercialized.
Three D−A−π−A organic dyes based on 5,6difluoro-2,1,3-benzothiadiazole (DFBTD) were synthesized by sequential direct arylation and characterized by spectroscopic and electrochemical techniques. Compared to 2,1,3-benzothiadiazole (BTD) analogue, the presence of two fluorine atoms on DFBTD results not only in a significant increase in the molar absorptivity but also in a blue shift of the onset of the absorption spectra. In the system of DFBTD-based sensitizers, replacing the thienyl unit bridge with disubstituted cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) further increases molar absorptivity and decreases the oxidation potential of the excited state E (s+/s*) . Similarly, changing the indoline donor to 4-butoxy-N-(4-butoxyphenyl)-N-phenylaniline increases the optical band gap and decreases the oxidation potential of the excited state E (s+/s*) of the sensitizer. The correlation between the molecular structure of these sensitizers and the photovoltaic performance of the dye cells were examined using current− voltage scan, incident photon to electron conversion efficiency (IPCE), femtosecond transient absorption spectroscopy (TAS), and electrochemical impedance spectroscopy (EIS). The observed change of the photovoltage and photocurrent upon changing the molecular structure of the sensitizers are discussed in terms of the charge injection from the excited state to the interband gap states of TiO 2 and the charge recombination between injected electrons into TiO 2 film and electrolyte. In all, it is found that the most efficient D−A−π−A dye achieved an open circuit voltage of 0.717 V, short circuit current density of 18.8 mA/cm 2 , corresponding to an overall power conversion efficiency of 9.1%.
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