Low-voltage low-power fully-integratable automatic gain controls

This paper discusses the design of low-voltage low-power fully-integratable automatic gain controls. Four different AGCs are presented, all consisting of three elementary building blocks: a controlled amplifier, a comparator and a voltage follower. Their design is treated separately. As an example, the final section describes an automatic gain control for hearing instruments, realized in a bipolar process.     

Measuring the External Quantum Efficiency of Two‐Terminal Polymer Tandem Solar Cells

Tandem configurations, in which two cells are stacked and connected in series, offer a viable approach to further increase the power conversion efficiency (PCE) of organic solar cells. To enable the future rational design of new materials it is important to accurately assess the contributions of individual subcells. Such accurate measurement of the external quantum efficiency (EQE) of the subcells of two‐terminal organic or polymer tandem solar cells poses specific challenges, caused by two characteristics of these cells, i.e. a sub‐linear light intensity dependence of the current and a field‐assisted charge collection. These properties necessitate that EQE experiments are carried out under representative illumination conditions and electrical bias to maintain short‐circuit conditions for the addressed subcell. We describe a method to determine the magnitudes of the bias illumination and bias voltage during EQE measurements, based on the behavior of single junction cells and optical modeling. The short‐circuit current densities of the subcells obtained by convolution of the EQE with the AM1.5G solar spectrum are consistent with those obtained from optical modeling and correctly predict the current density–voltage characteristics of the tandem cell under AM1.5G conditions.     

Multidimensional Nonlinear Schur Parametrization of NonGaussian Stochastic Signals. Part One: Statement of the Problem

The subject of this three-part paper is the multidimensional nonlinear Schur parametrization problem for higher-order (and non-Gaussian) stochastic signals. In the first part of this paper we state the nonlinear orthogonal parametrization problem as a generalization of the linear prediction/innovations filter problem. A unified geometric approach to the problem is introduced in the following three isometrically isomorphic spaces: of random variables (of higher-order stochastic sequences), of multi-indexed matrices, and of multidimensional z-polynomials. The nonlinear orthogonal approximate filters of the Volterra–Wiener class are considered. In the second part [30] of this paper we derive a generalized multidimensional nonlinear Schur parametrization algorithm for higher-order nonstationary stochastic sequences. The third part [33] of the paper is devoted to the complexity reduction problem in the nonlinear case, where a low-complexity Schur parametrization procedure, following from a nonlinear generalization of the staircase matrix extension problem [13], is proposed.     

Carbon‐Based Anodes for Lithium Sulfur Full Cells with High Cycle Stability

The lithium sulfur battery system has been studied since the late 1970s and has seen renewed interest in recent years. However, even after three decades of intensive research, prolonged cycling can only be achieved when a large excess of electrolyte and lithium is used. Here, for the first time, a balanced and stable lithium sulfur full cell is demonstrated with silicon–carbon as well as all‐carbon anodes. More than 1000 cycles, a specific capacity up to 1470 mAh g^?1 _sulfur (720 mAh g^?1 _cathode), and a high coulombic efficiency of over 99% even with a low amount of electrolyte are achieved. The alternative anodes do not suffer from electrolyte depletion, which is found to be the main cause of cell failure when using metallic lithium anodes.     

Normally Oriented Adhesion versus Friction Forces in Bacterial Adhesion to Polymer‐Brush Functionalized Surfaces Under Fluid Flow

Bacterial adhesion is problematic in many diverse applications. Coatings of hydrophilic polymer chains in a brush configuration reduce bacterial adhesion by orders of magnitude, but not to zero. Here, the mechanism by which polymer‐brush functionalized surfaces reduce bacterial adhesion from a flowing carrier fluid by relating bacterial adhesion with normally oriented adhesion and friction forces on polymer (PEG)‐brush coatings of different softness is studied. Softer brush coatings deform more than rigid ones, which yields extensive bond‐maturation and strong, normally oriented adhesion forces, accompanied by irreversible adhesion of bacteria. On rigid brushes, normally oriented adhesion forces remain small, allowing desorption and accordingly lower numbers of adhering bacteria result. Friction forces, generated by fluid flow and normally oriented adhesion forces, are required to oppose fluid shear forces and cause immobile adhesion. Summarizing, inclusion of friction forces and substratum softness provides a more complete mechanism of bacterial adhesion from flowing carrier fluids than available hitherto.     

Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance

Efficient organic electronic devices require a detailed understanding of the relation between molecular structure, thin film growth, and device performance, which is only partially understood at present. Here, we show that small changes in molecular structure of a donor absorber material lead to significant changes in the intermolecular arrangement within organic solar cells. For this purpose, phenyl rings and propyl side chains are fused to the diindenoperylene (DIP) molecule. Grazing incidence X-ray diffraction and variable angle spectroscopic ellipsometry turned out to be a powerful combination to gain detailed information about the thin film growth. Planar and bulk heterojunction solar cells with C60 as acceptor and the DIP derivatives as donor are fabricated to investigate the influence of film morphology on the device performance. Due to its planar structure, DIP is found to be highly crystalline in pristine and DIP:C60 blend films while its derivatives grow liquid-like crystalline. This indicates that the molecular arrangement is strongly disturbed by the steric hindrance induced by the phenyl rings. The high fill factor (FF) of more than 75% in planar heterojunction solar cells of the DIP derivatives indicates excellent charge transport in the pristine liquid-like crystalline absorber layers. However, bulk heterojunctions of these materials surprisingly result in a low FF of only 54% caused by a weak phase separation and thus poor charge carrier percolation paths due to the lower ordered thin film growth. In contrast, crystalline DIP:C60 heterojunctions lead to high FF of up to 65% as the crystalline growth induces better percolation for the charge carriers. However, the major drawback of this crystalline growth mode is the nearly upright standing orientation of the DIP molecules in both pristine and blend films. This arrangement results in low absorption and thus a photocurrent which is significantly lower than in the DIP derivative devices, where the liquid-like crystalline growth leads to a more horizontal molecular alignment. Our results underline the complexity of the molecular structure-device performance relation in organic semiconductor devices.     

Optical determination of the junction temperature of OLEDs

This paper describes a novel optical measurement technique for the in situ determination of the spatial temperature distribution at the organic layer level in large-area organic light-emitting diodes (OLEDs). The local junction temperature of OLEDs is a very important factor with respect to the luminance uniformity. Moreover the variation of local temperatures leads to a non-uniform depreciation of its light output, which in turn increases the luminance non-uniformity over time and affects the lifetime expectancy of the OLED.     

Renoprotective Angiographic Polymersomes

Computed tomography (CT) angiography is powerful for the diagnosis of vascular diseases. Unfortunately, this method usually requires a high dosage of iodinated contrast agents, which can lead to severe elevation of reactive oxygen species (ROS) levels within kidneys. This causes oxidative stress, apoptosis, and hence contrast-induced nephropathy (CIN), a leading cause of iatrogenic renal failure, especially for patients with renal insufficiency. Herein, a route is shown to circumvent such problems with the usage of rationally designed renoprotective angiographic polymersomes (RAPs) as blood pool CT contrast agents. RAPs are biodegradable nanoparticles prepared via self-assembly of poly(ethylene oxide)-block-poly(triiodobenzoic chloride-conjugated polylysine-stat-phenylboronic acid pinacol ester-conjugated polylysine) (PEO₄₅-b-P[(Lys-IBC)₄₅-stat-(Lys-PAPE)₁₅]). The key to the efficiency of such nanoparticles as renoprotective contrast agents arises from the rationally chosen repeat units: Lys-IBC exhibits a concentration-dependent X-ray attenuation capability and Lys-PAPE introduces an ROS-scavenging ability to the polymersome. The study shows that RAPs can reduce the risk of CIN in mice with kidney injury. Additionally, a 5-fold increase in angiographic live time is observed using RAPs, compared to commonly used iodinated small molecule contrast agents. In summary, a new strategy is proposed for the design of a renoprotective angiographic contrast agent that is capable of reducing the risk of CIN.