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It is certain that perovskite materials must be a game‐changer in the solar industry as long as their stability reaches a level comparable with the lifetime of a commercialized Si photovoltaic. However, the operational stability of perovskite solar cells and modules still remains unresolved, especially when devices operate in practical energy‐harvesting modes represented by maximum power point tracking under 1 sun illumination at ambient conditions. This review article covers from fundamental aspects of perovskite instability including chemical decomposition pathways under light soaking and electrical bias, to recent advances and techniques that effectively prevent such degradation of perovskite solar cells and modules. In particular, fundamental causes for permanent degradation due to ion migration and trapped charges are overviewed and explain their interplay between ions and charges. Based on the degradation mechanism, recent advances on the strategies are discussed to slow down the degradation during operation for a practical use of perovskite‐based solar devices. The operational stability of perovskite solar cells and modules is a key challenge which still remain unresolved. This review article discusses fundamentals of perovskite degradation due to different stresses including air molecules, light illumination, and electrical bias. The operational stability of these devices and recent advances to stabilize devices are overviewed on a way toward commercialization of perovskite solar devices.

The solution process has been employed to obtain Ruddlesden–Popper two-dimensional/three-dimensional (2D/3D) halide perovskite bilayers in perovskite solar cells for improving the efficiency and chemical stability; however, the solution process has limitations in achieving thermal stability and designing a proper local electric field for efficient carrier collection due to the formation of a metastable quasi-2D perovskite. Here we grow a stable and highly crystalline 2D (C 4 H 9 NH 3 ) 2 PbI 4 film on top of a 3D film using a solvent-free solid-phase in-plane growth, which could result in an intact 2D/3D heterojunction. An enhanced built-in potential is achieved at the 2D/3D heterojunction with a thick 2D film, resulting in high photovoltage in the device. The intact 2D/3D heterojunction endow the devices with an open-circuit voltage of 1.185 V and a certified steady-state efficiency of 24.35%. The encapsulated device retained 94% of its initial efficiency after 1,056 h under the damp heat test (85 °C/85% relative humidity) and 98% after 1,620 h under full-sun illumination. Two-dimensional structures introduced into perovskite solar cells improve performance yet their morphological and dimensional control remains challenging. Jang et al. devise a solid-phase approach to grow phase-pure two-dimensional perovskites over bulk perovskite, which affords greater device efficiency and stability.

To date, numerous biosensing platforms have been developed for assessing drug-induced cardiac toxicity by measuring the change in contractile force of cardiomyocytes. However, these low sensitivity, low-throughput, and time-consuming processes are severely limited in their real-time applications. Here, we propose a cantilever device integrated with a polydimethylsiloxane (PDMS)-encapsulated crack sensor to measure cardiac contractility. The crack sensor is chemically bonded to a PDMS thin layer that allows it to be operated very stably in culture media. The reliability of the proposed crack sensor has been improved dramatically compared to no encapsulation layer. The highly sensitive crack sensor continuously measures the cardiac contractility without changing its gauge factor for up to 26 days (>5 million heartbeats), while changes in contractile force induced by drugs are monitored using the crack sensor-integrated cantilever. Finally, experimental results are compared with those obtained via conventional optical methods to verify the feasibility of building a contraction-based drug-toxicity testing system. Measuring cardiac contractility is challenging. Here, the authors encapsulated a crack-based sensor with polydimethylsiloxane, thereby endowing the sensor with the stability to measure cardiac contractility for up to 26 days as well as monitoring drug-induced cardiac toxicity in cell culture.

A mechanical crack-based sensor inspired by the mechanism spiders use to sense minute variations in stress offers ultrahigh sensitivity to pressure and vibration and can easily be mounted on human skin for the purposes of speech recognition and the monitoring of physiological signals. Along came a spider-like strain sensor Usually when spiders are mentioned in a biomimetic context the remarkable tensile strength of spider silk is discussed. But in this study, Mansoo Choi and colleagues take inspiration from the slit sensory organs that a spider uses to detect vibrations in its web. The authors have developed a nanoscale mechanical crack-based sensor consisting of a thin platinum layer, in which tiny cracks are produced in a controlled way, on a flexible polymer sheet. Vibrations and changes in pressure are measured as changes in conductivity in the platinum sheet as the cracks open and close. The potential of the device is demonstrated with a variety of examples such as with a pixelated sensor that can detect a flapping ladybird and a flexible sensor that can measure and replay music. It can easily be mounted on human skin for purposes such as speech recognition and the monitoring of physiological signals. Recently developed flexible mechanosensors based on inorganic silicon 1 , 2 , 3 , organic semiconductors 4 , 5 , 6 , carbon nanotubes 7 , graphene platelets 8 , pressure-sensitive rubber 9 and self-powered devices 10 , 11 are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints 12 . Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider’s slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0–2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection–reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.

Perovskite solar cells have shown unprecedent performance increase up to 22% efficiency. However, their photovoltaic performance has shown fast deterioration under light illumination in the presence of humid air even with encapulation. The stability of perovskite materials has been unsolved and its mechanism has been elusive. Here we uncover a mechanism for irreversible degradation of perovskite materials in which trapped charges, regardless of the polarity, play a decisive role. An experimental setup using different polarity ions revealed that the moisture-induced irreversible dissociation of perovskite materials is triggered by charges trapped along grain boundaries. We also identified the synergetic effect of oxygen on the process of moisture-induced degradation. The deprotonation of organic cations by trapped charge-induced local electric field would be attributed to the initiation of irreversible decomposition. Improving the stability of perovskite solar cells remains crucial. Here, Ahn et al . show that trapped charges at grain boundaries induce the dissociation of the perovskite compound in the presence of moisture, and explain why degradation is irreversible under illumination and reversible in the dark.

The surfactant and colloidal nanoparticles has been considered for various applications because of interaction of both complex mixtures. The hydrophilic SiO 2 nanoparticle could not be surface active behavior at the liquid/air interface. In this study, the SiO 2 nanoparticles have been modified with 3-isocyanatopropyltriethoxy-silane (ICP), and the effect of foam stability has been investigated. The physical properties of surface modified SiO 2 nanoparticle were analyzed by XRD, TGA, FT-IR, and SEM. After surface modification of SiO 2 nanoparticles, the contact angle of SiO 2 nanoparticle was also increased from 62° to 82° with increased ICP concentration. The experimental result has shown that SiO 2 nanoparticle with ICP was positive effect and improved foam stability could be obtained at proper ICP concentration compared with un-modified SiO 2 nanoparticle.

All matter at finite temperatures emits electromagnetic radiation due to the thermally induced motion of particles and quasiparticles. Dynamic control of this radiation could enable the design of novel infrared sources; however, the spectral characteristics of the radiated power are dictated by the electromagnetic energy density and emissivity, which are ordinarily fixed properties of the material and temperature. Here we experimentally demonstrate tunable electronic control of blackbody emission from graphene plasmonic resonators on a silicon nitride substrate. It is shown that the graphene resonators produce antenna-coupled blackbody radiation, which manifests as narrow spectral emission peaks in the mid-infrared. By continuously varying the nanoresonator carrier density, the frequency and intensity of these spectral features can be modulated via an electrostatic gate. This work opens the door for future devices that may control blackbody radiation at timescales beyond the limits of conventional thermo-optic modulation. Graphene’s exotic properties make it suitable for many different optoelectronic devices. Brar et al . show that graphene plasmonic resonators can be exploited to produce narrow spectral emission in the mid-infrared, whose frequency and intensity can be modulated by electrostatic gating.

Perovskite solar cells have attracted significant research efforts due to their remarkable performance, with certified power conversion efficiency now reaching 22%. Solution-processed perovskite thin films are polycrystalline, and grain boundaries are thought to be responsible for causing recombination and trapping of charge carriers. Here we report an effective and reproducible way of treating grain boundaries in CH 3 NH 3 PbI 3 films deposited by means of a Lewis acid–base adduct approach. We show by high-resolution transmission electron microscopy lattice images that adding 6 mol% excess CH 3 NH 3 I to the precursor solution resulted in a CH 3 NH 3 I layer forming at the grain boundaries. This layer is responsible for suppressing non-radiative recombination and improving hole and electron extraction at the grain boundaries by forming highly ionic-conducting pathways. We report an average power conversion efficiency of 20.1% over 50 cells (best cell at 20.4%) together with significantly reduced current–voltage hysteresis achieved by this grain boundary healing process. The grain boundaries in thin-film perovskite solar cells are responsible for non-radiative carrier recombination, which is deleterious for the optoelectronic performance. Son et al.  show how to passivate the grain boundaries by using excess CH 3 NH 3 I in the precursor solution, achieving efficiencies of 20.4%.

Highlights Moth-eye structured polydimethylsiloxane (PDMS) films with different sizes were fabricated to improve the efficiency of perovskite solar cells. The PDMS with 300-nm moth-eye films significantly reduced light reflection at the front of the glass and therefore enhanced the solar cell efficiency of ~ 21%. The PDMS with 1000-nm moth-eye films exhibited beautiful coloration. Large-area polydimethylsiloxane (PDMS) films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells. An approach that incorporated photolithography, bilayer PDMS deposition and replication was used in the fabrication process. By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells, the optical properties of the devices could be tuned by changing the size of the moth-eye structures. The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~ 21% due to the antireflective effect of the moth-eye structure. Furthermore, beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect. Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.

Guided cracks were successfully generated in an electrode using the concentrated surface stress of a prism-patterned Nafion membrane. An electrode with guided cracks was formed by stretching the catalyst-coated Nafion membrane. The morphological features of the stretched membrane electrode assembly (MEA) were investigated with respect to variation in the prism pattern dimension (prism pitches of 20 μm and 50 μm) and applied strain ( S  ≈ 0.5 and 1.0). The behaviour of water on the surface of the cracked electrode was examined using environmental scanning electron microscopy. Guided cracks in the electrode layer were shown to be efficient water reservoirs and liquid water passages. The MEAs with and without guided cracks were incorporated into fuel cells, and electrochemical measurements were conducted. As expected, all MEAs with guided cracks exhibited better performance than conventional MEAs, mainly because of the improved water transport.