Current‐density–voltage (J–V) hysteresis in perovskite solar cells (PSCs) is a critical issue because it is related to power conversion efficiency and stability. Although parameters affecting the hysteresis have been already reported and reviewed, little investigation is reported on scan‐direction‐dependent J–V curves depending on perovskite composition. This review investigates J–V hysteric behaviors depending on perovskite composition in normal mesoscopic and planar structure. In addition, methodologies toward hysteresis‐free PSCs are proposed. There is a specific trend in hysteresis in terms of J–V curve shape depending on composition. Ion migration combined with nonradiative recombination near interfaces plays a critical role in generating hysteresis. Interfacial engineering is found to be an effective method to reduce the hysteresis; however, bulk defect engineering is the most promising method to remove the hysteresis. Among the studied methods, KI doping is proved to be a universal approach toward hysteresis‐free PSCs regardless of perovskite composition. It is proposed from the current studies that engineering of perovskite film near the electron transporting layer (ETL) and the hole transporting layer (HTL) is of vital importance for achieving hysteresis‐free PSCs and extremely high efficiency.

Visual inspection has traditionally been used for structural health monitoring. However, assessments conducted by trained inspectors or using contact sensors on structures for monitoring are costly and inefficient because of the number of inspectors and sensors required. To date, data acquisition using unmanned aerial vehicles (UAVs) equipped with cameras has become popular, but UAVs require skilled pilots or a global positioning system (GPS) for autonomous flight. Unfortunately, GPS cannot be used by a UAV for autonomous flight near some parts of certain structures (e.g., beneath a bridge), but these are the critical locations that should be inspected to monitor and maintain structural health. To address this difficulty, this article proposes an autonomous UAV method using ultrasonic beacons to replace the role of GPS, a deep convolutional neural network (CNN) for damage detection, and a geo‐tagging method for the localization of damage. Concrete cracks, as an example of structural damage, were successfully detected with 97.7% specificity and 91.9% sensitivity, by processing video data collected from an autonomous UAV.

A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI 3 ) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, the degradation mechanisms are revealed; a strong water adhesion following an elongated lead-iodine (Pb-I) bond distance is observed, which leads to a δ-phase transition on the (100) facet. Through engineering, a higher surface fraction of the (111) facet can be achieved, and the (111)-dominated crystalline FAPbI 3 films show exceptional stability against moisture. Our findings elucidate unknown facet-dependent degradation mechanisms and kinetics.

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Post-treatement of an unannealed perovskite film is found to be more efficienct way to passivate defects of perovskite solar cells.

Surface passivation of perovskite grains is one of the promising methods to reduce recombination and improve stability of perovskite solar cells (PSCs). We herein report the effect of a melaminium iodide additive on the photovoltaic performance of PSCs based on (FAPbI)(CsPbBr) perovskite. Cyclic -C═N- and primary amine in melamine are a good hydrogen bond acceptor and Lewis base, which can interact with both the organic cation and Lewis acidic lead iodide in the perovskite film. Melaminium iodide is synthesized and added to the precursor solution, which is directly spin-coated to form the perovskite film. The presence of melaminium iodide additive reduces the trap density from 1.02 × 10 to 0.645 × 10 cm, which leads to the reduction of nonradiative recombination and thereby improving the mean open-circuit voltage and the fill factor from 1.054 to 1.095 V and from 0.693 to 0.725 V, receptively. In addition, photocurrent-voltage hysteresis is reduced by the melaminium iodide additive, which results in an enhanced average power conversion efficiency, obtained from reverse and forward scanned data, from 15.86 to 17.32%. Time-resolved photoluminescence confirms that melaminium iodide plays a more important role in passivating the rear surface of the perovskite layer contacting the hole transporting spiro-MeOTAD layer. An aging test under a relative humidity of 65% reveals that melaminium iodide improves stability because of the suppression of the defect evolved by moisture.

These results suggest that having one or two copies of the A118G allele is common among Koreans and may be an important genetic factor in the etiology of alcohol dependence and the frequency of alcohol consumption.

At present, perovskite light-emitting diodes are mostly based on various forms of nanostructures exploiting their exciton confinement property. However, the few reports utilizing bulk or polycrystalline perovskites have been limited in application because of the difficulties of forming high-quality films, especially on the existing organic charge transport layers. When these charge transport organics are exchanged with thicker CH 3 NH 3 PbCl 3 , the emitting CsPbBr 3 thick polycrystalline films containing CH 3 NH 3 Br are conformally deposited with improved luminescence quality without driving voltage increase. Enhanced crystallinity and prolonged photoluminescence are observed by exploiting interfacial defect passivation and the strain-induced effect in the heterostructures. This approach could lead to high-performance light-emitting diodes and may also be extended to other perovskite devices.