Improved size distribution of AgBiS2 colloidal nanocrystals by optimized synthetic route enhances photovoltaic performance

Ternary silver bismuth sulfide (AgBiS₂) colloidal nanocrystals (NCs) have been recognized as a photovoltaic absorber for environmentally-friendly and low-temperature-processed thin film solar cells. However, previous synthetic methods involving hot injection of sulfur precursors into metal oleate precursor solutions do not provide a balance between nucleation and growth, leading to AgBiS₂ NCs with broad size distributions. Here, we demonstrate the modified synthetic route that size distribution of AgBiS₂ NCs can be improved by pre-adding the non-coordinating 1-octadecene (ODE) solvent into metal precursor solutions, leading to controlled concentration of coordinating oleic acid with improved hot-injection synthetic conditions. The addition of ODE as a non-coordinating solvent to metal precursor/oleic acid solution significantly suppresses variations in the concentration of coordinating oleic acid after injection of the sulfur precursor solution, leading to a homogenous reaction between the metal and sulfur precursors. For photovoltaic devices fabricated using the resultant AgBiS₂ NCs, the champion device shows power conversion efficiency (PCE) of 5.94% with an open-circuit voltage (V_OC) of 0.52 V. This performance is better than that a control device (PCE of 5.50% and V_OC of 0.49 V) because of the reduced energetic disorder and band tail broadening originating from the uniformly-sized AgBiS₂ NCs.     

Energy Saving Electrochromic Polymer Windows with a Highly Transparent Charge‐Balancing Layer

Highly transparent TiO₂ nanoparticles are explored as a non‐electrochromic (non‐EC) charge‐balancing layer for a high color contrast, bistable electrochromic window (ECW). The TiO₂ nanoparticle (TNP) layer increases the potential at the EC polymer electrode, thereby lowering the working voltage of the ECW. This leads to lower the power consumption of ECWs without loss in the high color contrast (ΔT > 72%) and to remarkably improve the cyclability (ΔT change <1% over 3000 cycles), mainly due to the low overvoltage (<0.1 V) on the electrochromic polymer layer. Furthermore, the ECWs including the non‐EC TNP layer show long‐term bistability (>2.7 h, 40% increase) and UV stability (ΔT change <1%) to provide a low‐power automatic ECW. This finding shows that the charge balanced ECP window has the potential to be used for an energy saving ECW with low‐power consumption and will be widely applied in various ECWs as well as electrochemical devices with multiple functions.     

Pseudohalide‐Exchanged Quantum Dot Solids Achieve Record Quantum Efficiency in Infrared Photovoltaics

Application of pseudohalogens in colloidal quantum dot (CQD) solar‐cell active layers increases the solar‐cell performance by reducing the trap densities and implementing thick CQD films. Pseudohalogens are polyatomic analogs of halogens, whose chemistry allows them to substitute halogen atoms by strong chemical interactions with the CQD surfaces. The pseudohalide thiocyanate anion is used to achieve a hybrid surface passivation. A fourfold reduced trap state density than in a control is observed by using a suite of field‐effect transistor studies. This translates directly into the thickest CQD active layer ever reported, enabled by enhanced transport lengths in this new class of materials, and leads to the highest external quantum efficiency, 80% at the excitonic peak, compared with previous reports of CQD solar cells.     

Assessing Effects of Task and Data Distribution on the Effectiveness of Visual Encodings

In addition to the choice of visual encodings, the effectiveness of a data visualization may vary with the analytical task being performed and the distribution of data values. To better assess these effects and create refined rankings of visual encodings, we conduct an experiment measuring subject performance across task types (e.g., comparing individual versus aggregate values) and data distributions (e.g., with varied cardinalities and entropies). We compare performance across 12 encoding specifications of trivariate data involving 1 categorical and 2 quantitative fields, including the use of x, y, color, size, and spatial subdivision (i.e., faceting). Our results extend existing models of encoding effectiveness and suggest improved approaches for automated design. For example, we find that colored scatterplots (with positionally‐coded quantities and color‐coded categories) perform well for comparing individual points, but perform poorly for summary tasks as the number of categories increases.     

A modified exhaustive search on a password system using SHA-1

In this paper, we show a method of exhaustive search on a password system that uses SHA-1 iteratively. Our method uses both the technique shown in Steube [16] and a technique for computing repetitions of SHA-1. Combining these two techniques reduces the total number of operations. We also show how to apply our method to MS Office (Microsoft Office) 2007/2010.     

Melt‐intercalation nanocomposites with fluorinated polymers and a correlation for nanocomposite formation

Various fluorinated polymers were investigated to produce polymer nanocomposites with special clays. Natural and organically treated montmorillonite clays were melt‐compounded with the polymers. Characterization by wide‐angle X‐ray scattering and transmission electron microscopy showed the separation of montmorillonite layers and the formation of polymer nanocomposites. Organically treated montmorillonite clay dispersed in poly(vinylidene fluoride) and various vinylidene fluoride copolymers and formed nanocomposites. Natural and organophilic clays were not well dispersed in other fluorinated copolymers and polyethylene. A correlation was developed for the formation of polymer–clay nanocomposite structures in chlorinated and fluorinated polymers in terms of the dielectric constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1061–1071, 2004     

Amine‐Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light‐Emitting Diodes

Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light‐emitting diodes (LED) are fabricated for the first time with solution‐processed polymer‐based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross‐linked PQDs. The brightest blue LED based on all inorganic CsPb(Br_1?xCl_x)₃ PQDs is also reported.     

Extraction and prioritization of product attributes using an explainable neural network

Pattern Analysis and Applications - Identification of product attributes is an important matter in real-world business environments because customers generally make purchase decisions based on...