photovoltaic technology, where lifetimes greater than 25 years are required. [2] Although the issue of device stability has attracted increased attention of the photovoltaic research community in the last two years, reports that systematically study the fundamental causes (e.g., heat, electrical stress, humidity, oxygen, (UV) light, chemical precursors, processing conditions, influence of film quality and morphology) and mechanisms limiting the material and device stability remain scarce. [2][3][4][5] While the degradation of methylammonium lead iodide (MAPbI 3 ) in humid air has been studied experimentally as well as theoretically and was long thought to be the main factor for material degradation in ambient environment, [6][7][8][9][10][11][12][13][14][15] studies exploring the influence of oxygen and light on the solar cell performance have only recently been reported. [16][17][18][19][20] It has been shown that photoexcited electrons in the perovskite layer can form superoxide (O 2 − ) via electron transfer to molecular oxygen, which through deprotonation of the methylammonium cation in turn results in irreversible material degradation. The severity of the degradation has been linked to the efficiency of electron extraction via the electron extracting layer (EEL): devices employing a compact-TiO 2 /mesoporous Al 2 O 3 or compact-TiO 2 as EELs degraded in dry air on a timescale of less than 1 h, while with the use of a mesoporous TiO 2 layer, an EEL which results in faster electron extraction, the lifetimes were significantly increased. However, in these reports only the degradation of complete photovoltaic device was reported, with limited information on the degradation of the perovskite active layer itself and the impact of its microstructure was not identified.In this work, we systematically study the degradation of MAPbI 3 films under precisely controlled exposure to various oxygen levels (0-20%) under simulated sunlight in order to shed light on the progression of perovskite degradation under these conditions. We investigate two types of perovskite layers that are formed using different fabrication methods. The two recipes allow us to include the effect of layer microstructure on the dynamics of oxygen-induced degradation. We characterize the electronic, optical, compositional, and structural properties of the degraded perovskite films and correlate these results This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI 3 ) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure-fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique-it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovsk...

Perovskite-based solar cells are promising because of their rapidly improving efficiencies but suffer from instability issues. Recently, it has been claimed that one of the key contributors to the instability of perovskite solar cells is ion migration-induced electrode degradation, which can be avoided by incorporating inorganic hole-blocking layers (HBLs) in the device architecture. In this work, we investigate the operational environmental stability of methylammonium lead iodide perovskite solar cells that contain either an inorganic or organic HBL, with only the former effectively blocking ions from migrating to the metal electrode. This is confirmed by X-ray photoemission spectroscopy measured on the electrodes of degraded devices, where only electrodes of devices with an organic HBL show a significant iodine signal. Despite this, we show that when these devices are degraded under realistic operational conditions (i.e., constant illumination in a variety of atmospheric conditions), both types of devices exhibit nearly identical degradation behavior. These results demonstrate that contrary to prior suggestions, ion-induced electrode degradation is not the dominant factor in perovskite environmental instability under operational conditions.

To use the “apparent diffusion coefficient” (Dapp) as a quantitative imaging parameter, well-suited test fluids are essential. In this study, the previously proposed aqueous solutions of polyvinylpyrrolidone (PVP) were examined and temperature calibrations were obtained. For example, at a temperature of 20°C, Dapp ranged from 1.594 (95% CI: 1.593, 1.595) μm2/ms to 0.3326 (95% CI: 0. 3304, 0.3348) μm2/ms for PVP-concentrations ranging from 10% (w/w) to 50% (w/w) using K30 polymer lengths. The temperature dependence of Dapp was found to be so strong that a negligence seems not advisable. The temperature dependence is descriptively modelled by an exponential function exp(c2 (T − 20°C)) and the determined c2 values are reported, which can be used for temperature calibration. For example, we find the value 0.02952 K-1 for 30% (w/w) PVP-concentration and K30 polymer length. In general, aqueous PVP solutions were found to be suitable to produce easily applicable and reliable Dapp-phantoms.

Magnetic sensors are widely used in our daily life for assessing the position and orientation of objects. Recently, the magnetic sensing modality has been introduced to electronic skins (e-skins), enabling remote perception of moving objects. However, the integration density of magnetic sensors is limited and the vector properties of the magnetic field cannot be fully explored since the sensors can only perceive field components in one or two dimensions. Here, we report an approach to fabricate high-density integrated active matrix magnetic sensor with three-dimensional (3D) magnetic vector field sensing capability. The 3D magnetic sensor is composed of an array of self-assembled micro-origami cubic architectures with biased anisotropic magnetoresistance (AMR) sensors manufactured in a wafer-scale process. Integrating the 3D magnetic sensors into an e-skin with embedded magnetic hairs enables real-time multidirectional tactile perception. We demonstrate a versatile approach for the fabrication of active matrix integrated 3D sensor arrays using micro-origami and pave the way for new electronic devices relying on the autonomous rearrangement of functional elements in space.

Many modern electronic applications rely on functional units arranged in an active‐matrix integrated on a single chip. The active‐matrix allows numerous identical device pixels to be addressed within a single system. However, next‐generation electronics requires heterogeneous integration of dissimilar devices, where sensors, actuators, and display pixels sense and interact with the local environment. Heterogeneous material integration allows the reduction of size, increase of functionality, and enhancement of performance; however, it is challenging since front‐end fabrication technologies in microelectronics put extremely high demands on materials, fabrication protocols, and processing environments. To overcome the obstacle in heterogeneous material integration, digital electrochemistry is explored here, which site‐selectively carries out electrochemical processes to deposit and address electroactive materials within the pixel array. More specifically, an amorphous indium‐gallium‐zinc oxide (a‐IGZO) thin‐film‐transistor (TFT) active‐matrix is used to address pixels within the matrix and locally control electrochemical reactions for material growth and actuation. The digital electrochemistry procedure is studied in‐depth by using polypyrrole (PPy) as a model material. Active‐matrix‐driven multicolored electrochromic patterns and actuator arrays are fabricated to demonstrate the capabilities of this approach for material integration. The approach can be extended to a broad range of materials and structures, opening up a new path for advanced heterogeneous microsystem integration.

No abstract

Self assembled catheters with deep sub-mm diameters deliver liquids, carry out micromanipulation, and sense magnetic fields.

Flexible electronics has gained tremendous attention over the past decades, revolutionizing fields such as telecommunication, multimedia, and healthcare. [1] Major electronic components, e.g., interconnects, antennas, diodes, and transistors, have been fabricated on thin polymeric foils to generate new options in the toolkit of developers. Applying thin polymeric foils as substrates facilitates the production of electronic systems with low weight, shape compliance, robustness, and reliability with ever-increasing complexity. The ultrathin design of these electronic devices has promoted bioelectronics that include artificial skins, [2] sensor arrays, [3] electronic implants such as brain probes, [4] and nerve cuffs, [5] to name a few. The ability to naturally conform to complex 3D shaped anatomies is a vital feature for electronic devices to interact with soft biological tissue. And while the shape of a large-area flexible electronic device can be easily adapted manually to the geometric requirements of the final application, handling becomes increasingly more challenging when aiming at smaller dimensions, when, e.g., a submillimeter nerve fiber bundle has to be enclosed gently with a similarly small cuff implant. [6] Shapeable microelectronic devices, which transform their shape on demand, provide an alternative strategy to accomplish this challenging task. [7] For instance, soft microscale structures with integrated electronic circuits have recently been demonstrated to wrap around peripheral nerves in situ when exposed to elevated temperatures or moisture. [8,9] These devices, however, lack the ability to reshape repeatedly and on demand in the operating environment. Such functionalities require the integration of biocompatible flexible shape and position sensors together with robust microactuators, fabricated ideally by a monolithic wafer-scale process.Among a variety of small-scale actuators that are driven by pneumatic [10,11] and hydraulic [12] pressure, electric [13] and