Understanding the Role of Grain Boundaries on Charge-Carrier and Ion Transport in Cs2AgBiBr6 Thin Films

Halide double perovskites have gained significant attention, owing to their composition of low-toxicity elements, stability in air, and recent demonstrations of long charge-carrier lifetimes that can exceed 1 µs. In particular, Cs₂AgBiBr₆ is the subject of many investigations in photovoltaic devices. However, the efficiencies of solar cells based on this double perovskite are still far from the theoretical efficiency limit of the material. Here, the role of grain size on the optoelectronic properties of Cs₂AgBiBr₆ thin films is investigated. It is shown through cathodoluminescence measurements that grain boundaries are the dominant nonradiative recombination sites. It also demonstrates through field-effect transistor and temperature-dependent transient current measurements that grain boundaries act as the main channels for ion transport. Interestingly, a positive correlation between carrier mobility and temperature is found, which resembles the hopping mechanism often seen in organic semiconductors. These findings explain the discrepancy between the long diffusion lengths >1 µm found in Cs₂AgBiBr₆ single crystals versus the limited performance achieved in their thin film counterparts. This work shows that mitigating the impact of grain boundaries will be critical for these double perovskite thin films to reach the performance achievable based on their intrinsic single-crystal properties.     

Functional Coatings on High‐Performance Polymer Fibers for Smart Sensing

Above a critical temperature, high‐performance fibers may lose their mechanical properties resulting in catastrophic events of damage when, e.g., used as load‐carrying ropes. Here, a method to functionalize polymer fibers with thermochromic optical coatings that enable signaling of damaging thermal history is introduced. These smart coatings are comprised of an index‐tunable anti‐reflection coating based on chalcogenide phase change materials (PCM). It is demonstrated that the insulator?metal phase transition of these materials can be aligned with the critical deterioration temperature of both polyethylene terephthalate (PET) monofilaments and liquid‐crystal polyester (LCP) yarns by composition tuning. The carefully designed optical system amplifies the change in optical properties of its constituents upon phase change. The thermal and mechanical degradation of these fibers can thus be monitored and displayed by eye.     

Highly Stable Contact Doping in Organic Field Effect Transistors by Dopant‐Blockade Method

In organic device applications, a high contact resistance between metal electrodes and organic semiconductors prevents an efficient charge injection and extraction, which fundamentally limits the device performance. Recently, various contact doping methods have been reported as an effective way to resolve the contact resistance problem. However, the contact doping has not been explored extensively in organic field effect transistors (OFETs) due to dopant diffusion problem, which significantly degrades the device stability by damaging the ON/OFF switching performance. Here, the stability of a contact doping method is improved by incorporating “dopant‐blockade molecules” in the poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) film in order to suppress the diffusion of the dopant molecules. By carefully selecting the dopant‐blockade molecules for effectively blocking the dopant diffusion paths, the ON/OFF ratio of PBTTT OFETs can be maintained over 2 months. This work will maximize the potential of OFETs by employing the contact doping method as a promising route toward resolving the contact resistance problem.     

A shirt containing multistage phase change material and active cooling components was associated with increased exercise capacity in a hot,humid environment

Recent advances in clothing design include the incorporation of phase change materials (PCM) and other active cooling components (ACC) to provide better body heat dissipation. The purpose of this study was to determine the effect of wearing a shirt containing multistage PCM/ACC on exercise capacity at low (5.0), moderate–high (7.5) and extreme (9.0) levels of the physiological strain index (PSI). Fourteen individuals tested two shirts (control vs. cooling) during 45-min of interval running in a hot, humid (35 ± 1 °C; 55 ± 6% RH) environment. The cooling shirt resulted in an 8% improvement in exercise capacity at a PSI of 7.5 (p < 0.05). The observed increase in exercise capacity would likely translate to a significant improvement in exercise performance. More research is needed to determine a best practice approach for the use of cooling clothing as a counter to exercise-induced heat exposure.

Practitioner Summary: In this report, we demonstrate that when forced to exercise in a hot, humid environment, an individual’s exercise capacity may increase by as much as 8% when wearing a shirt composed of multistage phase change material and active cooling components.     

Detection of X‐Rays by Solution‐Processed Cesium‐Containing Mixed Triple Cation Perovskite Thin Films

Materials and technology development for designing innovative and efficient X‐ray radiation detectors is of utmost importance for a wide range of applications ranging from security to medical imaging. Here, highly sensitive direct X‐ray detectors based on novel cesium (Cs)‐based triple cation mixed halide perovskite thin films are reported. Despite being in a thin film form, the devices exhibit a remarkably high X‐ray sensitivity of (3.7 ± 0.1) µC Gy^?1 cm^?2 under short‐circuit conditions. At a small reverse bias of 0.4 V, the sensitivity further increases by orders of magnitude reaching a record value of (97 ± 1) µC Gy^?1 cm^?2 which surpasses state‐of‐the‐art inorganic large‐area detectors (a‐Se and poly‐CZT). Based on detailed structural, electrical, and spectroscopic investigations, the exceptional sensitivity of the triple cation Cs perovskite is attributed to its high ambipolar mobility‐lifetime product as well as to the formation of a pure stable perovskite phase with a low degree of energetic disorder, due to an efficient solution‐based alloying of individual n‐ and p‐type perovskite semiconductors.     

Computational completeness of simple semi-conditional insertion–deletion systems of degree (2,1)

Natural Computing - Insertion–deletion (or ins–del for short) systems are simple models of bio-inspired computing. They are well studied in formal language theory, especially regarding...     

Activity in Boolean networks

In this paper we extend the notion of activity for Boolean networks introduced by Shmulevich and Kauffman (Phys Rev Lett 93(4):48701:1–4, 2004). In contrast to existing theory, we take into account the actual graph structure of the Boolean network. The notion of activity measures the probability that a perturbation in an initial state produces a different successor state than that of the original unperturbed state. It captures the notion of sensitive dependence on initial conditions, and provides a way to rank vertices in terms of how they may impact predictions. We give basic results that aid in the computation of activity and apply this to Boolean networks with threshold functions and nor functions for elementary cellular automata, d-regular trees, square lattices, triangular lattices, and the Erd?s–Renyi random graph model. We conclude with some open questions and thoughts on directions for future research related to activity, including long-term activity.     

Project report: Strong Writer

Review Essay

Project report: Strong Writer     

Nachweis und Identifizierung einer neuen Maillard-Verbindung in erhitzter Milch

Summary By means of polarography a new Maillard product (5a) was detected in heated milk. The compound was isolated from a glycine/lactose mixture, which had been heated in buffer at pH 6,8, and then freeze dried by extraction with ethylacetate/methanol. According to its spectroscopic properties,5a is 4-0--d-galactopyranosyl-2-hydroxy-2-methyl-2H-pyran-3-(6H)-one. Though the amount of5a formed during heat treatment of milk corresponds to the severity of heat stress, the usefulness of5a as an indicator with respect to intensity of heat treatment is limited.5a is rather rapidly converted to galactosyl isomaltol; also unknown peaks develop in the polarogram.Zusammenfassung Bei der Polarographie erhitzter Milch wurde ein bisher unbekanntes Maillard-Produkt (5a) entdeckt, es wurde aus einen Glycin/Lactose-Modellansatz durch Extraktion mit Essigester/Methanol sowie mehrmalige chromatographische Trennung isoliert. Die Strukturaufklärung des 4-0--d-Galaktopyranosyl-2-hydroxy-2-methyl-2H-pyran 3(6H)-ons (5a) gelang mit Hilfe der Spektraldaten. Obwohl sich die Menge von (5a) in einem bestimmten Temperaturbereich proportional zur Erhitzungsdauer entwickelt, ist (5a) infolge einer schnellen Umwandlung in Galaktosylisomaltol (12a) und durch das Entstehen von nicht identifizierten Störpeaks bei der Polarographie nicht als Indikationsubstanz für die Milcherhitzung geeignet.