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Perovskite solar cells show excellent power conversion efficiencies, long carrier diffusion lengths and low recombination rates. This encourages a view that intragrain defects are electronically benign with little impact on device performance. In this study we varied the methylammonium (MA)/formamidinium (FA) composition in MA1–xFAxPbI3 (x = 0–1), and compared the structure and density of the intragrain planar defects with device performance, otherwise keeping the device nominally the same. We found that charge carrier lifetime, open-circuit voltage deficit and current density–voltage hysteresis correlate empirically with the density and structure of {111}c planar defects (x = 0.5–1) and {112}t twin boundaries (x = 0–0.1). The best performance parameters were found when essentially no intragrain planar defects were evident (x = 0.2). Similarly, reducing the density of {111}c planar defects through MASCN vapour treatment of FAPbI3 (x ≈ 1) also improved performance. These observations suggest that intragrain defect control can provide an important route for improving perovskite solar cell performance, in addition to well-established parameters such as grain boundaries and interfaces. The role of intragrain planar defects in halide perovskite solar cell devices remains elusive. Now, Li et al. tune the composition of the perovskite layer to minimize the planar defect density and observe an improvement in the device performance.

The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic–inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se2 and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se2, and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed.

Summary The stability of perovskite solar cells (PSCs) has been considered as the largest obstacle to their commercialization. Herein, we observed that the main failure mechanism for MAPbI3 perovskite is the escape of methylammonium (MA) iodide at the grain boundaries in an open space or the reconstruction of crystal in a confined small space, as well as the irreversible long-distance ionic migration under the multiple actions of light, heat, and electrical bias. Strengthened with bifunctional organic molecular of 5-ammoniumvaleric acid (5-AVA) iodide at the grain boundaries, the MAPbI3 crystal was localized in the nanoscale, and thus, the decomposition or reconstruction was inhibited and the ionic migration became reversible. As a result, we propose a reliable approach to make PSCs meet stability standards of IEC61215:2016 qualification tests. A printable PSC filled with (5-AVA)XMA1-XPbI3 has been working for more than 9,000 h at a maximum power point of 55°C ± 5°C without obvious decay.

Cities are important barriers to protect people's lives and property in the face of natural disasters, economic fluctuations and epidemic diseases. The evaluation of urban resilience is a hybrid multiple attribute group decision-making problem involving both crisp and fuzzy indicators. In order to evaluate the urban resilience reasonably and quantitatively, an urban resilience evaluation index system is established, including four primary indicators of ecological environment, municipal facilities, economic development and social development, and 28 secondary indicators. An evaluation model based on the theory of intuitionistic fuzzy set and TOPSIS method is proposed. The intuitionistic trapezoidal fuzzy number is used to quantify the fuzzy index and determine the weights of experts. The weight of each index is determined based on the maximizing deviation method. The relevant data of Dalian City from 2013 to 2017 are collected to evaluate the city resilience, and a sensitivity analysis is carried out based on the proposed model. The results may provide insights for the further urban resilience promotion.

Perovskite solar cells (PSCs) have emerged as one of the most promising candidates for photovoltaic applications. Low-cost, low-temperature solution processes including coating and printing techniques makes PSCs promising for the greatly potential commercialization due to the scalability and compatibility with large-scale, roll-to-roll manufacturing processes. In this review, we focus on the solution deposition of charge transport layers and perovskite absorption layer in both mesoporous and planar structural PSC devices. Furthermore, the most recent design strategies via solution deposition are presented as well, which have been explored to enlarge the active area, enhance the crystallization and passivate the defects, leading to the performance improvement of PSC devices.

Organic solar cells have attracted academic and industrial interests due to the advantages like lightweight, flexibility and roll-to-roll fabrication. Nowadays, 18% power conversion efficiency has been achieved in the state-of-the-art organic solar cells. The recent rapid progress in organic solar cells relies on the continuously emerging new materials, device fabrication technologies, and the deep understanding on film morphology, molecular packing and device physics. Donor and acceptor materials are the key materials for organic solar cells since they determine the device performance. The past 25 years have witnessed an odyssey in developing high-performance donors and acceptors. In this review, we focus on those star materials and milestone work, and introduce the molecular structure evolution of the key materials. These key materials include homopolymer donors, D-A copolymer donors, A-D-A small molecule donors, fullerene acceptors and nonfullerene acceptors. At last, we outlook the challenges and very important directions in key materials development.

A medium-bandgap acceptor IBCT based on an 2-(1-oxo-1,2-dihydro-3H-benzo[b]cyclopenta[d]thiophen-3-ylidene)malononitrile end unit was developed. IBCT has an optical bandgap of 1.65 eV and afforded a power conversion efficiency of 11.26% and an open-circuit voltage of 1.02 V in single-junction organic solar cells when blending with a wide-bandgap copolymer donor L1. The L1:IBCT solar cell was further used as the front cell in tandem solar cells, yielding a 15.25% efficiency. IBCT is among the best medium-bandgap acceptors.

The direct band gap CsPbBr3 perovskite is regarded as a promising alternative for low-cost and high-performance X-ray radiation detectors. Despite the fact that CsPbBr3 nanocrystals have been shown to be good scintillators in the indirect conversion mode, the direct X-ray conversion with CsPbBr3 single crystals is expected to yield higher spatial resolution. Here, rubidium (Rb) doping is demonstrated to be an efficient approach to improve carrier transport and X-ray detection performance in the direct-conversion X-ray detectors based on Cs(1-x)RbxPbBr3 single crystals. Electrical properties' characterizations as combined with X-ray photoelectron spectroscopy (XPS) measurements have revealed that Rb doping in Cs(1-x)RbxPbBr3 single crystals can enhance the atomic interaction and orbital coupling between Pb and Br atoms, leading to an enhancement of carrier transport and X-ray detection performance. X-ray detectors based on a small amount (0.037%) of Rb-doped Cs(1-x)RbxPbBr3 single crystals exhibited a high X-ray sensitivity of 8097 μC Gyair-1 cm-2. This work offers a feasible strategy to improve the X-ray detection performance by chemical doping in all-inorganic perovskite X-ray detectors.

Owing to its nice performance, low cost, and simple solution-processing, organic-inorganic hybrid perovskite solar cell (PSC) becomes a promising candidate for next-generation high-efficiency solar cells. The power conversion efficiency (PCE) has boosted from 3.8% to 25.2% over the past ten years. Despite the rapid progress in PCE, the device stability is a key issue that impedes the commercialization of PSCs. Recently, all-inorganic cesium lead halide perovskites have attracted much attention due to their better stability compared with their organic-inorganic counterpart. In this progress report, we summarize the properties of CsPb(IxBr1−x)3 and their applications in solar cells. The current challenges and corresponding solutions are discussed. Finally, we share our perspectives on CsPb(IxBr1−x)3 solar cells and outline possible directions to further improve the device performance.

Identifying critical facilities in a water distribution system (WDS) from the standpoint of recovery resilience is significant for emergency inspection and restoration when a large-scale system disruption occurs. Taking a damaged pipeline into account, this paper proposes a framework for realizing criticality identification. The priority with which a damaged pipeline needs to be restored to minimize WDS service loss and the impact of delaying such priority on the loss of service are taken as criticality metrics. To acquire two metric values for each pipeline, a WDS recovery optimization problem, which integrates mechanical repair measures with hydraulic simulation, aimed at minimizing system service loss, is proposed and then solved by a genetic algorithm. Given the stochasticity of disruptions on a WDS, critical pipelines are identified by a stochastic scoring method, based on the statistical distribution of the two metrics obtained by stochastic sampling. An application of the framework to a case study of a WDS with simulated disruption scenarios distinguished pipelines critical to effective infrastructure restoration. Compared with models using network centrality and vulnerability-based metrics, the framework proposes a more reasonable way to measure facility criticality in terms of recovery resilience.

We present a study at both the device level and the interfacial analytic level on the light-induced degradation in the inverted CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) with an optimized structure, which is based on the Cu electrode and the charge transport layers of PTAA and Bphen. To accelerate the degradation process, the PSCs are exposed to concentrated sunlight of 2 suns with different illumination duration under the short-circuited condition. Compared to under the open-circuited condition, the PSCs presented here show a slightly more obvious decrease of power conversion efficiency (PCE) and a more distinct hysteresis with the time of light exposure. We infer that, under the short-circuited condition, the more dramatic migration of ions induced by photocurrents should result in greater ohmic dissipation and more trap states. But the weak degradation effects indicate that the devices still exhibit an unexpected photochemical stability against light exposure. Most importantly, there is a self-healing behavior to partly recover the degradation with the light exposure time of more than 8 h, which can be ascribed to the modification from the Cu electrode and the charge transport layers of PTAA and Bphen. Being wrapped tightly in these coverlayers, the possible volatile decomposition products are restrained inside of the MAPbI3 layers and converted back to MAPbI3 with a great probability.

With the rapid development of artificial intelligence, memristive devices capable of detecting, processing, and memorizing deep-ultraviolet (DUV) signals are very promising for encoding, recognizing, and performing solar-blind sensitive tasks. Here, we propose a DUV-triggered SnO2 nanowire synaptic transistor in which the programmable persistent photoconductivity (PPC) effect is used to mimic essential bio-synaptic behaviors. The bio-synapse-like behaviors, such as excitatory postsynaptic current (EPSC), paired pulse facilitation (PPF), and spike-timing dependence plasticity (STDP) (named the first law of synaptic plasticity) were investigated and imitated using various gate voltages. Larger gate bias permits a more significant transition from short-term (STP) to long-term plasticity (LTP). A detailed theoretical model is presented herein based on results from a systematic analysis of optoelectronic synaptic performances. Importantly, Pavlov's learning (classical conditioning) was conceptually demonstrated through DUV photoinduction. We also observed a novel situation where the memory effect was slightly inhibited when the devices were simultaneously stimulated by optical and electric pulses, allowing detection of temporally close, spatially distributed DUV incident signals. This approach opens up a new application domain for ultrafast, robust, and adaptive processing in future optoelectronic neural systems.

All highly-efficient organic-inorganic halide perovskite (OIHP) solar cells to date are made of polycrystalline perovskite films which contain a high density of defects, including point and extended imperfections. The imperfections in OIHP materials play an important role in the process of charge recombination and ion migration in perovskite solar cells (PSC), which heavily influences the resulting device energy conversion efficiency and stability. Here we review the recent advances in passivation of imperfections and suppressing ion migration to achieve improved efficiency and highly stable perovskite solar cells. Due to the ionic nature of OIHP materials, the defects in the photoactive films are inevitably electrically charged. The deep level traps induced by particular charged defects in OIHP films are major non-radiative recombination centers; passivation by coordinate bonding, ionic bonding, or chemical conversion have proven effective in mitigating the negative impacts of these deep traps. Shallow level charge traps themselves may contribute little to non-radiative recombination, but the migration of charged shallow level traps in OIHP films results in unfavorable band bending, interfacial reactions, and phase segregation, influencing the carrier extraction efficiency. Finally, the impact of defects and ion migration on the stability of perovskite solar cells is described.

This paper presents the robustness analysis of the interdependencies between urban critical infrastructures (CI) against cascade failures. An analytical approach based on the dynamic percolation theory was introduced to investigate the multilayer interactional CI networks and to predict the urban calamity spreading as illustrate with example of China. The synergetic effect of the functional and geographical interdependencies between the networks on cascade failures of CI was studied by comparing four relevance patterns: no interdependency, the functional interdependency, the geographical interdependency, and the functional with geographical interdependency, where three different attack strategies were simultaneously considered. The results indicate that the geographical interdependency has a remarkable influence on the robustness of networks compared with functional interdependency. Moreover, excavating the scope and extent of the impact of these interdependencies, one can also find that the power network basically governs the cascade failures of global systems in contrast with water or gas network.

This paper presents a study on the initial light-induced degradation in inverted CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) with a structure of indium tin oxide (ITO)/poly (bis(4-phenyl) (2,4,6-trimethylphenyl) amine) (PTAA)/MAPbI3/ [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/4,7-diphenyl-1, 10-phenanthroline (Bphen)/Cu under anoxic conditions. The pristine champion devices fabricated by our optimized techniques can achieve a power conversion efficiency (PCE) of ∼18% with a negligible hysteresis. Accelerated by exposure to concentrated sunlight of 200 mW/cm2, the short-term degradation tests show that the degradation effects of light exposure on the lattice and electronic structures of the MAPbI3 active layer are almost negligible and the photoelectric parameters of devices demonstrate superior photochemical stability against illumination, which can be ascribed to the introductions of the Cu electrode and the proper charge transport layers of PTAA and Bphen. As the MAPbI3 layers are integrated in devices and wrapped in these coverlayers, the volatile decomposition products originated from the photochemical reactions in MAPbI3 active layer should be restrained inside of the active layer and finally regenerated MAPbI3. Moreover, the Cu electrode strongly retards the photochemical reactions by restraining the diffusion of I− ions and further enhances photochemical stability of the devices.

Effect of film thickness of mesoporous carbon on power conversion properties of the hole-conductor-free mesoscopic perovskite solar cells is studied by varying the volume of carbon paste. It is observed that, with increment of the film thickness, perovskite crystallites become smaller; As for the performance parameters, open-circuit voltage (VOC) drops slowly; while short-circuit current density (JSC) and fill factor (FF) rise at first, and then decrease after the film thickness surpasses about 22 μm. The slight decrease in open-circuit voltage (VOC) is due to heavier recombination brought by smaller crystallite size of perovskite. The upgraded short-circuit current density is due to accelerated charge-extracting rate across the interface between perovskite and mesoporous carbon, as revealed by the transient photocurrent (TPC) decay measurement. As for the improved fill factor, it is ascribed to the increased conductivity of the mesoporous carbon film. Besides, shelf-stability of the devices is tested. Stability up to 112 days (relative humidity of 40–70%, no encapsulation) are observed for these carbon based mesoporous perovskite solar cells, even though the mesoporous carbon is as thin as ∼4 μm. The sound stability shows that the TiO2 nanoparticle-bonding carbon film could provide effective barrier against H2O/O2.

Identifying the origin of intrinsic instability for organic–inorganic halide perovskites (OIHPs) is crucial for their application in electronic devices, including solar cells, photodetectors, radiation detectors, and light-emitting diodes, as their efficiencies or sensitivities have already been demonstrated to be competitive with commercial available devices. Here we show that free charges in OIHPs, whether generated by incident light or by current-injection from electrodes, can reduce their stability, while efficient charge extraction effectively stabilizes the perovskite materials. The excess of both holes and electrons reduce the activation energy for ion migration within OIHPs, accelerating the degradation of OIHPs, while the excess holes and electrons facilitate the migration of cations or anions, respectively. OIHP solar cells capable of efficient charge-carrier extraction show improved light stability under regular operation conditions compared to an open-circuit condition where the photo-generated charges are confined in the perovskite layers., Optoelectronic devices based on organic–inorganic halide perovskites show promising performance, but their poor stability impedes the commercialization. Here Lin et al. show that excess free charges are detrimental and efficient charge-carrier extraction is necessary for improved device stability.

Effect of the loading of perovskite crystallites on the power conversion properties of carbon based hole-conductor-free mesoscopic perovskite solar cells is studied by varying the concentration of the perovskite precursor from 0.3 to 1.0 mol/L (at given volume of 30 μL). It is observed that, when the concentration is 0.3 mol/L, poor filling is obtained due to relatively low loading of perovskite, and the perovskite solar cells suffer from huge dispersion in efficiencies and large hysteresis index (averaged at 18.29% and up to 34.61%). With increment of the concentration (from 0.4 to 1.0 mol/L), crystallinity of perovskite crystallites is improved according to X-ray diffraction studies, and the lifetime of photo-generated charge carriers is prolonged as reflected by transient photovoltaic (TPV) detection. Meanwhile, the open circuit voltage rises up from 0.86 (±0.03) V to 0.91 (±0.01) V, and the hysteresis index is reduced from 10.02 (±4.67)% to 1.45 (±2.21)%. However, the film conductance of carbon film is decreased due to the loading of perovskite, which deteriorates the fill factor of the devices. Finally, optimized power conversion efficiency is achieved at moderate concentration or 0.6 mol/L, which is 12.59 (±0.40) %, compared to 11.81 (±0.36) % at 1.0 mol/L. Due to the barrier provided by the carbon film against H2O/O2, all of the devices showed good shelf-stability, though loading of perovskite is varied in these devices.

Planar heterojunction (PHJ) organic photodetectors are potentially more stable than traditional bulk heterojunction counterparts because of the absence of uncontrolled phase separation in the donor and acceptor binary blend system. This work reports a new class of PHJ organic photodetectors based on the medium-band gap fullerene C60 and low-band gap fused-ring non-fullerene acceptor ID-MeIC bilayer structure, which allows a wide range of spectral response tuning across the UV-visible-near-infrared (UV-vis-NIR) region by tailoring individual layer thickness. The C60 layer not only increases the external quantum efficiency at 745 nm by 57% but also reduces dark currents by two orders of magnitude. More importantly, the p-type poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzi] is found to be the key compound to conduct the layer-by-layer fabrication as combined with n-type ID-MeIC for higher charge extraction efficiency. In light of the above information, PHJ organic photodetectors exhibited a specific detectivity of 6.5 × 1010 Jones to detect NIR light at 745 nm under -0.1 V. The linear dynamic range was estimated to be 80 dB. This work has demonstrated a feasible approach to develop a PHJ architecture with tunable spectral response in the UV-vis-NIR range toward long-term stable organic photodetectors for potential applications in flexible and wearable biomedical sensors.

Tailoring the organic spacing cations enables developing new Ruddlesden–Popper (RP) perovskites with tunable optoelectronic properties and superior stabilities. However, the formation of highly crystallized RP perovskites can be hindered when the structure of organic cations become complex. Strategies to regulate crystal growing process and grains quality remain to be explored. In this study, mixing Rb+ ions in precursor solution is reported to significantly promote the crystallinity of phenylethylammonium (PEA+) based RP perovskites without impacting on the major orientation of perovskite grains, which leads to increased power conversion efficiencies from 12.5% to 14.6%. It is found that the added Rb+ ions prefer to accumulate at crystal growing front and form Rb+ ions‐rich region, which functions as mild crystal growth inhibitor to retard the absorption and diffusion of organic cations at growing front and hence regulates crystal growing rate. The retarded crystal growth benefits PEA‐based RP perovskite films with elevated crystal qualities and prolonged carrier recombination lifetimes. Similar increased crystallinity and photovoltaic performance are achieved in other RP perovskites with non‐linear organic cations such as phenylmethylammonium (PMA+), 1‐(2‐naphthyl)‐methanammoniun (NMA+) by adding Rb+ ions, demonstrating using a small amount of growth inhibitor as a general route to regulate crystal growth., Besides achieving large grains by reducing the nucleation centers, controlling the crystal growth rate is another key issue to pursue high crystallinity. The crystal quality of quasi‐2D perovskite can be substantially improved by adding a small amount of growth inhibitors (i.e., Rb+ ions) in the precursor solution, which dynamically accumulate in the crystal growth front and retard the crystal growth rate.

The mixed caesium and formamidinium lead triiodide perovskite system (Cs1−xFAxPbI3) in the form of quantum dots (QDs) offers a pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective oleic acid (OA) ligand-assisted cation-exchange strategy that allows controllable synthesis of Cs1−xFAxPbI3 QDs across the whole composition range (x = 0–1), which is inaccessible in large-grain polycrystalline thin films. In an OA-rich environment, the cross-exchange of cations is facilitated, enabling rapid formation of Cs1−xFAxPbI3 QDs with reduced defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that the QD devices exhibit substantially enhanced photostability compared with their thin-film counterparts because of suppressed phase segregation, and they retain 94% of the original PCE under continuous 1-sun illumination for 600 h.

TiO2 is a famous electron-transport-material (ETM) that used widely in perovskite solar cells. Photo-catalysis effect is a highly concerned issue for such TiO2 based devices because of its impact on device stability. To deal with the problem, a strategy was proposed to passivate the surface of TiO2 by a thin layer of in-situ formed SnO2, and then perovskite solar cells (PSCs) were prepared using such modified TiO2. It was observed that, after the surface passivation, photo-to-electric power conversion efficiency, hysteresis as well as stability of the TiO2 based PSCs were all improved. For example, efficiency increased from 14.92 (±1.86)% (AM 1.5G, 100 mW/cm2) to 16.33 (±0.26)%; hysteresis index decreased from 20.49 (±11.85)% to 1.40 (±0.01)%. As for stability, after being stored for 25 days (relative humidity of about 45%, no encapsulation), efficiency could preserve 73.99% of the original value, comparing to 47.55% for device based on bare TiO2. Moreover, the passivation was found to accelerate electron extraction, while retard charge recombination between perovskite and TiO2. The improvement was ascribed to the enhanced contact between perovskite and bottom electron-transport-material, passivated surface defects of TiO2 by SnO2, as well as the high mobility of SnO2. Finally, designated ultraviolet (UV) illumination experiment showed that SnO2 passivation could obviously retard the photo-catalysis activity of TiO2, thus improve the UV stability of the devices.

Efficient and stable hole-conductor-free mesoscopic perovskite solar cells were fabricated using SiO2 as blocking layer which was inserted between the top carbon electrode and bottom electron-transport-layer in the device. Power conversion efficiency of 13.09% (AM1.5G, 100 mW/cm2) was obtained, which was comparable to those using ZrO2 as the blocking layer. Besides that, prolonged stability has been obtained. After being stored at ambient air for 104 days (relative humidity between 50% and 70%), 94.19% of the starting efficiency was preserved for devices without any encapsulation. Moreover, effect of thickness of SiO2 blocking layer on device performance was studied by tuning the concentration of SiO2 paste. A moderate concentrate was found to be beneficial to device performance. Without blocking layer, poor performance was observed due to short cutting between top electrode and bottom electron-transport-layer; when concentration of SiO2 paste is relative higher (which corresponded to relatively thicker films), cracks appeared which caused short-cutting. Finally, due to the relative higher preservation of Si element (more than 1000 times of Zr) in earth, applying SiO2 as blocking layer could further lower down the cost of the carbon based hole-conductor-free mesoscopic perovskite solar cells.

Flexible perovskite solar cells were prepared using two-step solution-processed SnO2 layers as electron-transport-material. The first layer was constructed by hydrothermal derived SnO2 nanoparticles, and the second layer was in-situ formed from hydrolysis and oxidization of SnCl2. It was observed that the two-step formed SnO2 layers could efficiently improve the device performance of the flexible perovskite solar cells. Without such layers, no photovoltaic effect was observed due to poor wettability of substrate. After SnO2 was deposited, power conversion begins due to improved crystallinity of perovskite layer. Compared with one-step processed SnO2 layer, the two-step processed SnO2 layers could take the advantages of accelerated charge extraction, lowered contact resistance, as well as reduced charge recombination, which help to upgrade open circuit voltage, short circuit current, fill factor and power conversion efficiency of the flexible devices. Device efficiency of 15.21% (AM 1.5 G, 100 mW/cm2) was obtained for the flexible devices, with prolonged shelf-stability in addition. After being stored in dark for 111 days (relative humidity of 35–55%, no encapsulation was used), device could keep 85% of starting efficiency. Meanwhile, specific power (ratio between power and device weight) of 0.87 kW/kg was obtained, as well as sound fatigue ability against bending. The solution based two-step formation process thus provides a reliable strategy for future application of flexible perovskite solar cells.

The power grid is a critical component of city infrastructure. If it is damaged by an earthquake, there can be a huge impact on the safety and well-being of society and individuals. Identifying nodes in the grid that are highly vulnerable to earthquake damage is significant for effective pre-earthquake damage prevention, emergency response, and post-earthquake relief. Three indicators, the probability of node disconnection, the node hierarchical level, and the node critical threshold, were chosen, and their combined ability to represent node vulnerability to damage from an earthquake event was analyzed. A variable fuzzy clustering model was used to classify and order the nodes in the grid. The 20-node power grid of a city was used as an example to show how highly vulnerable nodes were identified, and how the reasons for the high vulnerability of these nodes were drawn out of the analysis. Countermeasures were given to reduce network vulnerability. The variable fuzzy clustering method used in this paper offers a new perspective on network vulnerability, and it quantifies the vulnerability of grid nodes more comprehensively than existing methods of assessing grid vulnerability. This research is significant as a baseline reference for future studies of grid vulnerability.

Efficient and stable planar hole-transport-layer-free perovskite solar cells were fabricated using low temperature processed tin dioxide (SnO2, 180 °C) as electron-transport-material and carbon film (100 °C) as top electrode. Open circuit voltage of 1.03 ± 0.02 (highest at 1.07) V was obtained, which was 100 mV higher than that of reference devices using conventional high-temperature-processed mesoporous TiO2 as electron-transport-material, or 0.91 ± 0.03 (highest at 0.96) V. The increased open circuit voltage along with slightly-upgraded fill factor then helped to upgrade power conversion efficiency to 13.21 ± 0.7% (highest at 14.5%) under simulated illumination of AM 1.5 G, 100 mW/cm2, compared to 10.13 ± 1.34% (highest at 10.46%) of the reference devices. The improvement is ascribed to the upgraded built-in potential. Mott–Schottky study showed that, using low-temperature-processed SnO2 as electron-transport-material, higher built-in-potential (0.94 V) could be obtained, compared with 0.89 V of TiO2 based device, which then retarded charge recombination and thus increased both of the open circuit voltage and fill factor. Meanwhile, stability was test. Without any encapsulation, storage stability up to 150 days (3600 h, the test is still on-going) has been obtained for devices kept in dark (relative humidity ∼45%), which is contributed by the low photo-activity SnO2, and the adoption of formamidinium cations, bromide anions co-doped perovskite film.

A heptacyclic carbon–oxygen-bridged ladder-type unit, COi7, was designed. Two corresponding nonfullerene acceptors, COi7IC and COi7DFIC, were developed. The single crystal structure of COi7IC indicates an S-shaped backbone and a packing via π–π interaction of the end groups. PTB7-Th:COi7DFIC solar cells gave a power conversion efficiency of 8.32%, with a decent fill factor of 71.9%.

A carbon-oxygen-bridged ladder-type donor unit (CO5) was invented and prepared via an intramolecular demethanolization cyclization approach. Its single crystal structure indicates enhanced planarity compared with the carbon-bridged analogue indacenodithiophene (IDT). Owing to the stronger electron-donating capability of CO5 than IDT, CO5-based donor and acceptor materials show narrower bandgaps. A donor-acceptor (D-A) copolymer donor (PCO5TPD) and an A-D-A nonfullerene acceptor (CO5IC) demonstrated higher performance than IDT-based counterparts, PIDTTPD and IDTIC, respectively. The better performance of CO5-based materials results from their stronger light-harvesting capability and higher charge-carrier mobilities.

Using TiO2 nanoparticles as binders, highly conductive carbon films were prepared and used to fabricate monolithic hole-conductor-free perovskite solar cell in air. Carbon films were condensed by dehydration reaction between surface hydroxyls from both TiO2 nanoparticles and carbon particles, which is beneficial for adhesion ability and conductivity of carbon film, and the formation and filling properties of perovskite crystallites in the monolithic structure of “FTO/C TiO2/M-TiO2/M-ZrO2/Carbon” (C-Compact, M-Mesoporous). A reduced sheet resistance from 10 to 2.74 Ω/sq was obtained for carbon films annealed under relatively low temperature annealing. Confined distribution of perovskite crystallites in the region containing M-TiO2/M-ZrO2 layers and bottom of carbon film was obtained from 350 °C annealing, which helped to achieve upgraded power conversion efficiency (reverse scan) from 5.40 (±1.32) % to 9.21(±1.04) % (averaged) and 11.07% (champion) at testing area of ∼0.18 cm2, as well as stability of 1000 h in relative high humidity environment (RH:70–90%). The air-compatible fabrication process, sound device ability as well as low-cost of carbon materials make such monolithic device structure realistic candidate for mass production of perovskite solar cells.

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The manipulation of crystal orientation from the thermodynamic equilibrium states is desired in layered hybrid perovskite films to direct charge transport and enhance the perovskite devices performance. Here we report a templated growth mechanism of layered perovskites from 3D-like perovskites which can be a general design rule to align layered perovskites along the out-of-plane direction in films made by both spin-coating and scalable blading process. The method involves suppressing the nucleation of both layered and 3D perovskites inside the perovskite solution using additional ammonium halide salts, which forces the film formation starts from solution surface. The fast drying of solvent at liquid surface leaves 3D-like perovskites which surprisingly templates the growth of layered perovskites, enabled by the periodic corner-sharing octahedra networks on the surface of 3D-like perovskites. This discovery provides deep insights into the nucleation behavior of octahedra-array-based perovskite materials, representing a general strategy to manipulate the orientation of layered perovskites., The orientation of layered perovskites plays a crucial role in their charge transport behavior and hence, the efficiency of related solar cells. Here, the authors find that preformed 3D-like perovskites can efficiently template the growth of layered perovskites and determine their orientation.

Controllable synthesis of tin-doped all-inorganic perovskite (e.g. CsPb1-XSnXBr3) nanocrystals while maintaining tin at the divalent state is of great importance for tuning their optoelectronic properties by changing the chemical composition and geometrical size; however, this remains a non-negligible challenge. In contrast to the conventional high-temperature (>150 °C) synthesis reaction that would more likely facilitate oxidation of divalent Sn2+ to quadrivalent Sn4+, this work demonstrates a facile low-temperature (105-150 °C) hot-injection method to synthesize quantum-confined Sn2+-doped CsPb1-XSnXBr3 nanocrystals with sizes ranging from ∼6.2 nm to ∼8.3 nm depending on the reaction temperature. The optimized reaction temperature of 135 °C led to a Sn2+-doping ratio of 3.4% in CsPb1-XSnXBr3 nanocrystals which exhibited uniform nanoplatelets with an average lateral size of ∼7.4 nm. Furthermore, for the first time, we show that the perovskite nanocrystals are promising for the development of low-cost and trap-assisted photomultiplication UV-photodetectors, and the photodetectors based on CsPb0.966Sn0.034Br3 nanocrystals exhibited wavelength-dependent detectivities in the magnitude of 1011 Jones for UV light extending from 310 nm to 400 nm at a reverse bias of -7 V. The high EQE of ∼1940% at around 340 nm indicates that the devices had a gain at the large reverse bias condition, which is attributed to the formation of interfacial traps by CsPb0.966Sn0.034Br3 nanocrystals that can make the electron injection barrier thin enough to allow electron tunneling in the photodetectors for photomultiplication.

Regulating the crystallization of donor and acceptor to maintain balanced carrier mobility is of great importance to fabricate efficient organic solar cells (OSCs). Herein, the balanced crystallinity between donor and acceptor was finely controlled in blade-coated OSCs. By adding high crystalline FOIC into PBDB-T:ITIC system, a balanced carrier mobility was achieved, resulting in the much improved fill factor. The optimized ternary device exhibits an increased current density, due to the enhanced light-harvesting efficiency with complementary absorption and the morphology change. Morphology characterization demonstrated that the ternary film exhibits a highly balanced crystallinity between the donor and acceptor on account of the formation of acceptor alloy. Moreover, the ternary film not only possesses a small domain size, but also exhibits a high domain purity as compared to both binary films. Encouragingly, a highest power conversion efficiency (PCE) of 10.68% was obtained for the blade-coated ternary OSCs. In addition, the blade-coated flexible large-area (105 mm2) OSC based on PBDB-T:ITIC:FOIC ternary system also exhibits a high PCE of 9.81%, showing great potential in the high-throughput fabrication of OSCs.

Land comprehensive carrying capacity (LCCC) reflects the limits of urban development that the land ground in the spatial area can bear under the constraints of society, economy, resources, and environment. An accurate and objective evaluation of LCCC is of great significance to the rational planning of urban space. Using the entropy method to obtain the weights of evaluation indexes, this study constructed an index system composed of four subsystems, i.e., urban construction (UC), social economy (SE), industry development (ID), and urban ecology (UE). Furthermore, calculating the index of 11 cities for the Harbin-Changchun urban agglomeration (HCUA) to analyze the influence of LCCC from diverse dimensions for the period 2004&ndash, 2015. Lastly, the spatial and temporal differentiation characteristics between the neighboring units of LCCC were visualized through global and local spatial analysis. The results infer some novel findings as follows. (1) The overall tendency of the LCCC of the HCUA has gradually increased over the time window with the coordination of each subsystem. The urban ecological subsystem shows the highest rate of contribution and the social economy subsystem has the largest increase. Urban construction and industry development have a lower number of hot spot cities and lower clustering characteristics than social economy and urban ecology. (2) The core cities of the HCUA, Changchun and Harbin, demonstrate the reverse trend from 2010 to 2015, which reveals the states of excellent and good carrying capacity, respectively. In contrast, four cities are at the inferior state, and three cities are poor. Prioritizing the promotion of the industry development subsystem should be considered for these seven cities. (3) There is some spatial variation of LCCC in the HCUA, which shows the characteristic of &ldquo, gradually decreasing from the core city to the surrounding area&rdquo, Changchun and Jilin are high&ndash, high clustering areas that drive Siping from a cold spot to a hot spot. Focusing on the development of secondary growth pole cities, Jilin and Songyuan are forming complementary and mutual reinforcement with the core cities, which has a positive significance in promoting the sustainable development of the regional space of urban agglomeration.

The mechanism that how noncovalent conformation locks (NCLs) to improve the photovoltaic performance of polymer donors was investigated. By developing a model system with three structure-related copolymers W1, W2 and W3, a clear correlation was found between the locking strength in polymer backbone and the photovoltaic performance. W1 with the strongest S⋅⋅⋅O and F⋅⋅⋅H double-side locking gave the highest power conversion efficiency (PCE) of 16.23%, while W2 with a S⋅⋅⋅O single-side locking and W3 with a weakened S⋅⋅⋅O locking caused by Cl–H steric repulsion gave lower PCEs of 11.73% and 0.92%, respectively. With the aid of single crystal X-ray diffraction analysis, density functional theory calculation, grazing-incidence wide-angle X-ray scattering analysis, atomic force microscope study and device characterization, the functions of NCLs in improving the planarity, packing, crystallinity and hole mobility of polymers, as well as the morphology of blend films, were illuminated in detail.

A low-temperature fabrication routine is developed for hole-conductor-free and mesoscopic perovskite solar cells using a TiO2 nanoparticle-binding carbon electrode as the top electrode. Vacuum treatment is adopted to help the infiltration and formation processes of the organic–inorganic hybrid perovskite crystallites. It is observed that such treatment not only condenses the mesoporous skeleton and improves film conductance of the carbon electrode but also makes the perovskite crystallites grow in the core part of the mesoporous skeleton. As such, the extraction process of photogenerated charge carriers is accelerated due to the strengthened interfacial contact between the perovskite crystallites and the skeleton. Accordingly, the photo-to-electric power conversion efficiency of the low-temperature devices is upgraded from 7.38 (±1.40)% to 10.17 (±0.86)% (optimized at 12.29%, AM 1.5 G, 100 mW/cm2). In addition, prolonged stability is observed. Due to the condensed device structure, storage stability of 225 days has been achieved in ambient air (with relative humidity of about 40–60%), even without encapsulation. The proposed strategy is helpful in further reducing the production cost.

Organometal trihalide perovskites (OTPs) are arising as a new generation of low-cost active materials for solar cells with efficiency rocketing from 3.5% to over 20% within only five years. From "dye" in dye sensitized solar cells (DSSCs) to "hole conductors" and "electron conductors" in mesoscopic heterojunction solar cells, there has been a dramatic conceptual evolution on the function of OTPs in photovoltaic devices. OTPs were originally used as dyes in Gratzel cells, achieving a high efficiency above 15% which, however, did not manifest the excellent charge transport properties of OTPs. An analogy of OTPs to traditional semiconductors. was drawn after the demonstration of highly efficient planar heterojunction structure OTP devices and the observation of their excellent bipolar transport properties with a large diffusion length exceeding 100 nm in CH3NH3PbI3 (MAPbI(3)) polycrystalline thin films. This review aims to provide the most recent advances in the understanding of the origin of the high OTP device efficiency. Specifically, we will focus on reviewing the progress in understanding (1) the characterization of fantastic optoelectronic property of OTPs, (2) the unusual defect physics that originate the optoelectronic property, (3) morphology control of the perovskite film from fabrication process and film post-treatment, (4) device interface and charge transport layers that dramatically impact device efficiency in the OTP thin-film devices, (5) photocurrent hysteresis, (6) tandem solar cells and (7) stability of the perovskite materials and solar cell devices. (C) 2016 Elsevier B.V. All rights reserved.

Organometal trihalide perovskites (OTPs) are emerging as very promising photovoltaic materials because the power conversion efficiency (PCE) of OTP solar cells quickly rises and now rivals with that of single crystal silicon solar cells after only five-years research. Their prospects to replace silicon photovoltaics to reduce the cost of renewable clean energy are boosted by the lowtemperature solution processing as well as the very low-cost raw materials and relative insensitivity to defects. The flexibility, semitransparency, and vivid colors of perovskite solar cells are attractive for niche applications such as built-in photovoltaics and portable lightweight chargers. However, the low stability of current hybrid perovskite solar cells remains a serious issue to be solved before their broad application. Among all those factors that affect the stability of perovskite solar cells, ion migration in OTPs may be intrinsic and cannot be taken away by device encapsulation. The presence of ion migration has received broad attention after the report of photocurrent hysteresis in OTP based solar cells. As suggested by much direct and indirect experimental evidence, the ion migration is speculated to be the origin or an important contributing factor for many observed unusual phenomenon in OTP materials and devices, such as current−voltage hysteresis, switchable photovoltaic effect, giant dielectric constant, diminished transistor behavior at room temperature, photoinduced phase separation, photoinduced self-poling effect, and electrical-field driven reversible conversion between lead iodide (PbI2) and methylammonium lead triiodide (MAPbI3). Undoubtedly thorough insight into the ion-migration mechanism is highly desired for the development of OTP based devices to improve intrinsic stability in the dark and under illumination. In this Account, we critically review the recent progress in understanding the fundamental science on ion migration in OTP based solar cells. We look into both theoretical and experiment advances in answering these basic questions: Does ion migration occur and cause the photocurrent hysteresis in perovskite solar cells? What are the migrating ion species? How do ions migrate? How does ion migration impact the device efficiency and stability? How can ion migration be mitigated or eliminated? We also raise some questions that need to be understood and addressed in the future.

A narrowband red-light nanocomposite photodetector with gain is presented based on the polymer and fullerene derivative incorporating inorganic quantum dots. The introduced trap-induced hole injection dramatically improves the specific detectivity by 20-fold. A remarkable achievement is obtained with simultaneously increased linear dynamic range to 110 dB and improved noise equivalent power to 5 pW cm(-2).

For the fabrication of large-area devices, achieving both excellent photovoltaic performance and device stability simultaneously is the key to commercialization of organic solar cells (OSCs). Herein, non-fullerene OSCs with various additives (1,8-diiodooctane (DIO), 1,8-octanedithiol (ODT), chloronaphthalene (CN)) were fabricated by blade-coating in ambient environment. It was demonstrated that all these three additives can improve device performance. However, CN based device shows only a slightly increased power conversion efficiency (PCE) of 9.34% as compared to the device without additive (PCE = 9.19%). Although DIO based device presents an increased PCE of 9.87%, the corresponding device stability is poor. Impressively, due to the enhanced crystallization as well as the small and pure domains, the device with ODT additive not only possesses higher photovoltaic performance (PCE of 10.20%), but also exhibits better device stability. In addition, ODT based large-area device (90 mm2) prepared by blade-coating also exhibits a high PCE of 8.59%, showing great potential in fabricating efficient and stable large-area organic solar cells.

CH3NH3PbI3 (MAPbI3)-based perovskite solar cells (PSCs) with special hole and electron transport layers (HTL and ETL) were prepared to study their light-induced degradation. Obvious degradation was observed under initial light exposure not only at the device level but also at the film morphology and electronic structure level. Device performance parameters, such as short-circuit current (JSC), power conversion efficiency, fill factor, and hysteresis effect, were aggravated with an initial light exposure of less than ∼8 h at 1 sun intensity. Meanwhile, the deteriorated crystallinity and electronic structure of the MAPbI3 film were also detected with x-ray diffraction, ultraviolet photoelectron spectroscopy, and UV-Visible absorption spectroscopy. The observed degradation is rationally related to the light-induced decomposition of MAPbI3. However, the degradation can be partly recovered with the following light exposure resulting in self-healing of the devices and MAPbI3 films. The self-healing behavior should be ascribed to the conversion of decomposition products back to MAPbI3, because the intermediates are wrapped tightly in the photoactive layer by the compact coverlayers of HTLs and ETLs and some reversible reactions occur consequently. The mechanism of self-healing is discussed by introducing the trapped states derived from ion migration. The PSCs prepared here imply a good optical stability and thus a good performance facilitated by tight wrapping of the active MAPbI3.

Perovskite solar cells, bearing the merits of facile preparation and remarkable efficiency, has great potential for bringing the photovoltaic industry to a new generation. The photovoltaic market demands high-efficiency, high stability and low-cost fabrication of perovksite solar cells, especially stability to the humid environment for operation. Here, MAPbI3/agarose photoactive material for humid stable unencapsulated devices has been proposed. These solar cells have been operated in ambient humid environment without glove box, exhibiting efficiency up to 14.66% and retain 90% of its PCE after 1392 h and 60% of initial PCE after 1972 h in ambient humid environment (RH>70%) without encapsulation. FTIR and XPS measurements reveal two critical factors for the improved stability. The molecular level interactions between agarose and MAPbI3 passivates the grain boundaries of perovskite thus preventing its degradation. Moreover, the formation of Li+-agarose complex at the interface between perovskite layer and hole conductive layer, effectively prevents the water uptake of MAPbI3 layer. Both effects of passivation and minimization of hygroscopicity of LiTFSI by agarose lower the decomposition speed of perovskite, which obviously increases the power efficiency and stability of device.

The usage of TiO2 in perovskite solar cells is always faced with the risk of device decomposition due to its high photocatalysis activity. To deal with this problem, here in this work, a strategy of in situ surface passivation was proposed and performed on TiO2. After spin-coating Ca(OH)2 solution on a TiO2 mesoporous scaffold and annealing, the surface layer of the scaffold was converted into CaTiO3, as confirmed by X-ray photoemission spectroscopy and X-ray diffraction studies. The modified TiO2 scaffold was then used as an electron-transport-material in perovskite solar cells. It was observed that after moderate modification, the short-circuit current density increased from 22.32 (±0.25) to 23.19 (±0.28) mA/cm2, the open-circuit voltage rose from 1.042 (±0.009) to 1.080 (±0.011) V, and the fill factor increased from 63.89 (±1.95)% to 71.37 (±0.43)%, leading to an improvement from 14.92 (±0.36)% to 17.88 (±0.37)% of the power conversion efficiency. Transient photocurrent/photovoltage decay curves and impedance spectroscopy tests showed that moderate modification accelerated charge extraction while it retarded charge recombination. Besides, the in situ CaTiO3 layer prolonged the device stability. After being stored in the dark for 46 days (relative humidity of 30%), 92.6% of the initial efficiency was reserved, compared to that of 68.4% for the control devices. Designated UV irradiation showed that the surface passivation retarded the photocatalysis activity of TiO2, which contributed to the prolonged device stability.

Recently, acceptor-donor-acceptor (A-D-A) small molecules have emerged as promising nonfullerene acceptors (NFAs) for organic solar cells and have attracted great attention. The carbon-bridged (C-bridged) ladder-type D unit plays a crucial role in developing high-performance A-D-A NFAs. However, the medium electron-donating capability of C-bridged units is unfavorable for making NFAs with strong light-harvesting capability. In this regard, carbon-oxygen-bridged (CO-bridged) ladder-type units present advantages in developing strong light-absorbing NFAs. Here, recent progress in the newly emerging CO-bridged NFAs is highlighted. The synthetic methods for the polycyclic CO-bridged building blocks are introduced. The photovoltaic performance for CO-bridged NFAs is summarized and discussed. Perspectives on developing high-performance CO-bridged-NFA-based solar cells are made.

Because of the fast expansion of artificial intelligence, development and applications of neuromorphic systems attract extensive interest. In this paper, a highly interconnected neuromorphic architecture (HINA) based on flexible self-supported multiterminal organic transistors is proposed. Au electrodes, poly(3-hexylthiophene) active channels, and ion-conducting membranes were combined to fabricate organic neuromorphic devices. Especially, freestanding ion-conducting membranes were used as gate dielectrics as well as support substrates. Basic neuromorphic behavior and four forms of spike-timing-dependent plasticity were emulated. The fabricated neuromorphic device showed excellent electrical stability and mechanical flexibility after 1000 bends. Most importantly, the device structure is interconnected in a way similar to the neural architecture of the human brain and realizes not only the structure of the multigate but also characteristics of the global gate. Dynamic processes of memorizing and forgetting were incorporated into the global gate matrix simulation. Pavlov's learning rule was also simulated by taking advantage of the multigate array. Realization of HINAs would open a new path for flexible and sophisticated neural networks.

In this paper, we originally present a memristor-based chaotic oscillator which comes from the classical Chua circuit and is devoted to weak signal detection application. On this basis, a non-autonomous memristor-based chaotic oscillator is proposed to estimate the amplitude of weak character signals at diverse frequency, enhance signal-to-noise ratio (SNR) and especially implement square wave signals detection. The detection properties utilizing the proposed oscillator and those of the traditional chaotic oscillators have been compared to demonstrate that this novel oscillator has superior detection performance on strong anti-noise characteristics, detection sensitivity and so on. As a result, the proposed memristor-based chaotic oscillator for weak signal detection has a wide range of engineering applications.

This Review summarizes advances in understanding the unique physical properties of hybrid perovskites that enable the fabrication of high-efficiency solar cells with high open-circuit voltages, which is crucial for their further development towards commercialization.

Understanding the influence of light on ion migration in organic–inorganic halide perovskite (OIHP) materials is important to understand the photostability of perovskite solar cells. We reveal that light could greatly reduce the ion migration energy barrier in both polycrystalline and single crystalline OIHP. The activation energies derived from conductivity measurement under 0.25 Sun decrease to less than one half of the values in the dark. A typical ion drift velocity in CH3NH3PbI3 polycrystalline films is 1.2 μm s−1 under 1 Sun, compared with 0.016 μm s−1 under 0.02 Sun. Ion migration across the photoactive layers in most OIHP devices thus takes only subseconds under 1 Sun illumination, which is much shorter than what it was thought to take. Most important of all, ion migration through a single crystal surface is still too slow to be observed even after illumination for two days due to the large ion diffusion activation energy, >0.38 eV.