Coated and Printed Perovskites for Photovoltaic Applications

Hybrid organic–inorganic metal halide perovskite semiconductors provide opportunities and challenges for the fabrication of low‐cost thin‐film photovoltaic devices. The opportunities are clear: the power conversion efficiency (PCE) of small‐area perovskite photovoltaics has surpassed many established thin‐film technologies. However, the large‐scale solution‐based deposition of perovskite layers introduces challenges. To form perovskite layers, precursor solutions are coated or printed and these must then be crystallized into the perovskite structure. The nucleation and crystal growth must be controlled during film formation and subsequent treatments in order to obtain high‐quality, pin‐hole‐free films over large areas. A great deal of understanding regarding material engineering during the perovskite film formation process has been gained through spin‐coating studies. Based on this, significant progress has been made on transferring material engineering strategies to processes capable of scale‐up, such as blade coating, spray coating, inkjet printing, screen printing, relief printing, and gravure printing. Here, an overview is provided of the strategies that led to devices deposited by these scalable techniques with PCEs as high as 21%. Finally, the opportunities to fully close the shrinking gap to record spin‐coated solar cells and to scale these efficiencies to large areas are highlighted.     

Modified mason model for bulk acoustic wave resonators

Accurate modeling of a bulk acoustic wave resonator frequency response is limited by the inability of the current 1-D models to simulate certain parasitic modes excited in realistic 3-D structures. A simple technique is proposed to simulate such parasitic modes by employing the 1-D Mason Model of a resonator and a coupling term between the fundamental mode and those parasitic modes. This Modified Mason Model allows accurate simulation of resonators with arbitrary impedance and arbitrary resonating frequency. Finally, the model's prediction is compared with the on-wafer measurement of a ladder-type filter composed of several resonators.     

Polymeric anodes from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) for 3.5% efficient organic solar cells

We present highly efficient indium tin oxide free polymer solar cells based on poly-(3-hexylthiophene-2,5-diyl) and C₆₁-bis-butric-acid-methyl-ester (P3HT:bisPCBM) comprising a polymeric anode from highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) formulations. The film conductivity was optimized by various additives. We found conductivities of almost 600 S/cm upon the addition of dimethylsulfoxide. The wetting properties of different PEDOT:PSS formulations were investigated by contact angle measurements. The optimized high conductivity in combination with the good film forming properties allow for the fabrication of highly efficient organic solar cells with an external power conversion efficiency of 3.5% with PEDOT:PSS as polymeric anode.     

Observing Internet Worm and Virus Attacks with a Small Network Telescope

A network telescope is a portion of IP address space dedicated to observing inbound internet traffic. The purpose of a network telescope is to detect and log malicious traffic which originates from internet worms and viruses. In this paper, we investigate the statistical properties of observed traffic from a passive Class C telescope over a total of three months. We observe that only a few IP sources and destination ports are responsible for the majority of the traffic. We also demonstrate various ways to visualise the traffic profile from a telescope. We show that specific profiles can identify and distinguish portscans, hostscans and distributed denial-of-service (DDOS) attacks. Looking at the inter-arrival time of packets, the power spectrum and the detrended fluctuation analysis of the observed traffic, we show that there is very little sign of long-range dependence. This is in stark contrast to other network traffic and presents exciting possibilities for identifying malicious traffic purely from its traffic profile.     

General quantitative specification theories with modal transition systems

This paper proposes a new theory of quantitative specifications. It generalizes the notions of step-wise refinement and compositional design operations from the Boolean to an arbitrary quantitative setting. Using a great number of examples, it is shown that this general approach permits to unify many interesting quantitative approaches to system design.     

High aspect ratio multi-level mold inserts fabricated by mechanical micro machining and deep etch X-ray lithography

Complex microstructures can be fabricated in large quantities by thermoplastic molding processes. The shape of the microstructures is determined mainly by the mold insert. Until now, multi-level mold inserts have been fabricated either by deep etch X-ray lithography and electroforming, Harmening et al. (1992), or by milling of a brass substrate, Schaller et al. (1995). In both cases there are limitations on structuring either by the fabrication effort or by the sizes of the smallest available milling heads. To avoid these limitations on structuring, a new process for manufacturing multi-level mold inserts has been developed at Forschungszentrum Karlsruhe. Milling, drilling, deep etch X-ray lithography and electroforming have been combined to manufacture a mold insert which is characterized by high aspect ratios with small lateral dimensions and various level heights. Samples with two levels and an aspect ratio of 15 have been manufactured. Much higher aspect ratios seem to be achievable. This paper covers the fabrication process, first tests, and experimental results of manufacturing a multi-level mold insert for molding three-dimensional components of a microvalve system. The development of this technology has been supported by the European Community as part of the Esprit project IMICS.     

Color-Selective Printed Organic Photodiodes for Filterless Multichannel Visible Light Communication

Future lightweight, flexible, and wearable electronics will employ visible-light-communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength-selective bulk-heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light-management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge-carrier dynamics enabling state-of-the-art responsivities >10² mA W⁻¹ and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible-light-communication system capable of demultiplexing intermixed optical signals.     

Application of Thermodynamic Model for Inclusion Control in Steelmaking to Improve the Machinability of Low Carbon Free Cutting Steels

Oxide inclusions formed during steelmaking processes influence the machinability of steel products. At moderate and high cutting speeds, the tool life is dominated by chemical wear. However this wear can be suppressed by engineering exogenous and indigenous glassy oxide inclusions in steel. The present work demonstrates a method to engineer glassy oxide inclusions in a low carbon free cutting steel applying a new thermodynamic model for deoxidation control of steel based on slag‐melt as well as melt‐oxide inclusion equilibration. The model is used online in an industrial production line for the controlled production of glassy inclusions. These inclusions are shown to improve machinability by lubricating the tool‐chip interface during machining of the steel at high cutting speeds. Using an inclusion engineered work piece, the crater wear of an uncoated P10 tool is significantly improved and the tool life is tripled at cutting speeds in the range between 200 and 400 m/min. The industrial results show that thermodynamic modelling is a powerful tool to produce free cutting steels with consistently good machinability behaviour.