Layered metal halide perovskites have attracted enormous research attention over the last few years, befitting their unique optical and electronic properties. Low‐dimensional layered perovskites demonstrate great potential for various optoelectronic and sensing applications beyond photovoltaics. Herein, the recent progress and opportunities in 2D and quasi‐2D perovskites for light‐emitting diodes (LEDs), lasers, memristors, neuromorphic/synaptic applications, UV–vis photodetection, X‐ray detection, scintillators, and photocatalytic applications are reviewed. First, the crystal structure, characteristics, and fundamental properties of 2D layered perovskites are discussed. Recent efforts and developments of 2D and quasi‐2D metal halide perovskite for light‐emitting applications with excellent luminescence properties are reviewed. Unique properties of 2D perovskites, such as negligible leakage current due to restricted carrier transport, high stability, and hydrophobicity, make them viable for memristor devices. After discussing the memristor and neuromorphic devices using 2D perovskites, the outstanding performance of 2D perovskites in UV–vis photodetection including polarization‐sensitive photodetection is discussed. 2D perovskites recently proved as a superior candidate in X‐ray detection with high stability. Further, the scintillation properties of 2D perovskites for the detection of ionizing radiation are discussed. Finally, some of the very recent achievements and present future outlook, including exciting opportunities in this burgeoning field are highlighted.

Herein, we investigate the role of Eu3+ doping on CH3NH3PbBr3 nanoplatelets (NPLs) in terms of their optoelectronic properties and photodetection application through a combined experimental and theoretical approach. The introduction of EuCl3 in the CH3NH3PbBr3 crystal structure by a facile solvothermal method enabled the tuning of the lateral and vertical dimensions of the NSs to form large-area NPLs and finally monolayer nanocrystals. The appearance of low-angle diffraction peaks with Eu doping, which are observed in layered perovskite structures, confirms the formation of quasi-2D NPLs. The bandgap of the Eu-doped mixed halide perovskite systematically increases from 2.39 eV to 2.94 eV with increasing doping concentration. Interestingly, 10 mol% EuCl3 doping in the pure CH3NH3PbBr3 crystal dramatically enhances its absorbance and photosensitivity, resulting in high-performance photodetection. Under 405 nm excitation, the CH3NH3Pb0.9Eu0.1Br2.7Cl0.3 photodetector exhibits self-biased behavior with an on/off ratio >103, which is very significant. The planar device achieves a responsivity as high as 5.29 A W- and a detectivity of 1.06 × 1012 Jones under 405 nm with a power density of 0.14 mW cm-2 at 5 V. In addition, the device exhibits very fast response time with a rise/fall time of 17.5/38.5 μs, which is ∼4 times faster than the pristine CH3NH3PbBr3 counterpart. A linear relationship of photocurrent with light intensity in the CH3NH3Pb0.9Eu0.1Br2.7Cl0.3 photodetector signifies low recombination or charge trapping loss. High-performance photodetection in the Eu-doped device is ascribed to the elimination of trap states and the fast charge transfer process. To obtain better insight into the doped system, DFT analysis of the electronic structure of EuCl3-doped CH3NH3PbBr3 was performed and the results are fully consistent with the experimental findings. It was revealed that EuCl3 doping increases the density of states near the conduction band along with a blue shift in the bandgap as compared to that of the pristine perovskite, which in turn increases the built-in potential of the fabricated device, resulting in self-biased photodetection. This work paves the way for deeper understanding of lanthanide doping in perovskites and self-biased photodetection applications of a new family of Eu-doped mixed halide perovskite nanostructures.

Neuromorphic Computing Thin-film of lead-free caesium copper antimony chloride (Cs4CuSb2Cl12) layered double perovskite nanocrystals is utilized to demonstrate robust electroforming free analog resistive switching with synaptic functionalities and neural activities, as depicted in article number 2200562 by Sumaiya Parveen, Bikas C. Das, and co-workers.

The past decade has witnessed tremendous progress in metal halide perovskites, particularly in lead (Pb) halide perovskites, because of their extraordinary performance in cutting-edge optoelectronic devices. However, the toxicity of Pb and the environmental stability of the perovskites are two major issues that this field is currently facing. In recent years, 2D layered perovskites have emerged as a promising alternative to the traditional 3D perovskites due to their structural flexibility and higher environmental stability, though they lack the desired level of device efficiency. Doping with target ions can drastically tune the crystal structure, optical properties, charge recombination dynamics, and electronic properties of the 2D perovskite. Although the field of doping in 2D perovskites has seen substantial growth in recent times, no comprehensive review is available on the recent advances in doping of 2D perovskites and its effect on the optoelectronic properties. In this review, we summarize the progress in doping in 2D perovskites based on different doping sites including progress in different synthesis strategies and their impact on crystal structures and various optoelectronic properties. We then highlight the recent achievements in doped 2D perovskites for photovoltaic, LED and other emerging applications. Finally, we conclude with the challenges and the future scope in the doping studies of 2D layered perovskites, which need to be addressed for further developments of next-generation 2D perovskite-based optoelectronic devices.

Brain‐inspired artificial neural networks and neuromorphic computing are taking space to a new height based on solid‐state memristor devices. Despite considerable progress already made, the use of lead‐free double perovskite materials with direct bandgap can be recognized as a significant paradigm shift in this field. Here, growth, thin film deposition, and analog electroforming‐free resistive switching property along with promising artificial synaptic and neural activities of lead‐free layered cesium copper antimony chloride (Cs4CuSb2Cl12 or CCAC) double perovskite nanocrystals are reported. Optical and structural characterizations of CCAC microcrystals (MCs) and nanocrystals (NCs) confirm the growth, the existence of direct bandgap, and <111> oriented monoclinic crystal phase of space group C2/m. Interestingly, both the MCs and NCs display an almost equal bandgap of 1.1 eV in thin film even though they have higher bandgaps of 1.3 and 2.2 eV in dispersion, respectively. However, devices of NC thin film exhibit superior memristor behavior along with emulation of various synaptic and neural activities due to having less number of defects. Finally, the analog modulation of synaptic weight using CCAC memristor, in terms of postsynaptic currents, during potentiation and depression represents a significant achievement toward hardware implementation of neural networks and neuromorphic computing.

Cerium and terbium doping at high concentrations in organic–inorganic halide perovskite 2D nanosheets enables a stable deep blue emission with unity quantum yield.

Nonvolatile resistive switching based memristor and memtransistor devices have emerged as a leading platform in neuromorphic computing. In this work, we have fabricated a multifunctional synaptic transistor (ST) using a conjugated polymer P3HT channel and a superionic rubidium silver iodide (RbAg4I5) thin film coated over a polyethylene oxide (PEO) layer as the gate dielectric. Large hysteresis in the transfer curve represents the memristive behavior with at least 105 current On/Off ratio. Enormously large specific capacitance induced by the electrical double layers at the interfaces of PEO/RbAg4I5 dielectric induces polaron (P3HT+) generation in the channel through bound states formation by the electrons with Ag+ ions and consequent movement of iodine (I−) counter ions toward the P3HT channel under a negative gate bias stress. This is strongly supported by the blue shift of the Raman peak from 1444.2 to 1447.9 cm−1 and the appearance of a new peak at 1464.6 cm−1. Interestingly, the proposed ST device exhibits various synaptic actions, which include an excitatory postsynaptic current, paired-pulse facilitation, and short-term potentiation to long-term potentiation after repeated rehearsal on top of standard nonvolatile data storage capability. Our ST also depicts an enhanced retention to 103 s and more than 103 discrete On- and Off-states during potentiation and depression function modulation, respectively, just by consuming a very low energy of about 2.0 pJ per synaptic event. These results are very significant to make this organic synaptic transistor as a potential candidate in terms of the desired metrics for neuromorphic computation at low cost and improved accuracy in the future.

Precise control of the thickness of large-area two-dimensional (2D) organometal halide perovskite layers is extremely challenging owing to the inherent instability of the organic component. Herein, a novel, highly reproducible, and facile solvothermal route is reported to synthesize and tailor the thickness and optical band gap of the organic-inorganic halide perovskite nanosheets (NSs). Our study reveals that self-assembly of randomly oriented perovskite nanorods leads to the growth of multilayered perovskite NSs at ∼100 °C, while at higher temperature, large-area few-layer to bilayer 2D NSs (CH3NH3PbBr3) are obtained through lattice expansion and layer separation depending precisely on the temperature. Interestingly, the thickness of the 2D NSs shows a linear dependence on the reaction temperature and thus enables precise tuning of the thickness from 14 layers to 2 layers, giving rise to a systematic increase in the band gap and appearance of excitonic absorption bands. Quantitative analysis of the change in the band gap with thickness revealed a strong quantum confinement effect in the 2D layers. The perovskite 2D NSs exhibit tunable color and a high photoluminescence (PL) quantum yield (QY) up to 84%. Through a careful analysis of the steady-state and time-resolved PL spectra, the origin of the lower PL QY in thinner NSs is traced to surface defects in the 2D layers, for the first time. A white light converter was fabricated using the composition-tuned 2D CH3NH3PbBrI2 NS on a blue light-emitting diode chip. The 2D perovskite photodetector exhibits a stable and very fast rise/fall time (24 μs/103 μs) along with high responsivity and detectivity of ∼1.93 A/W and 1.04 × 1012 Jones, respectively. Storage, operational, and temperature-dependent stability studies reveal high stability of the 2D perovskite NSs under the ambient condition with high humidity. The reported method is highly promising for the development of large-area stable 2D perovskite layers for various cutting-edge optoelectronic applications.

Herein, we elucidate the origin of high photoluminescence quantum yield (PL QY) and high surface-enhanced Raman scattering (SERS) sensitivity of in-situ nitrogen-doped graphene quantum dots (N-GQDs). We show that the doping of heteroatoms in GQDs facilitates the excited-state charge transfer and improved recombination in N-GQDs yielding a PL QY of similar to 34%. Our study reveals that growth of GQDs in dimethyformamide solvent enables the reduction of the nonradiative sites in N-GQDs and the rearrangement of the charge distribution in the graphitic plane. Further, we demonstrate N-GQDs as an efficient SERS substrate with an enhancement factor of 3.2 x 10(3) with 10(-4) M RhB target, which is similar to 7-fold higher than the previous reports. The comparative studies of the SERS for undoped and N- and S-doped GQDs allow us to assess the contribution of the Forster resonance energy transfer (FRET) and chemical enhancement (CM) factors. Further, by controlling the functional groups of N-GQDs with vacuum annealing, and with different laser excitations, we isolate the contributions of CM and FRET, for the first time. The optimized N-GQDs exhibits a SERS detection limit of 10(-10) M for RhB. Finally, N-GQDs combined with RhB is utilized to demonstrate a white light emitter with a CIE coordinate (0.30, 0.34). (C) 2020 Elsevier Ltd. All rights reserved.

We elucidate the growth kinetics and scaling behavior of vacuum deposited CH3NH3PbBr3 thin film on various substrates and correlate the same with its microstructural and optical properties. Analysis of the AFM images reveals an abrupt change in the grain features for thickness, d >= 40 nm. Based on the evaluation of the scaling parameters, the perovskite films exhibit an anomalous scaling behavior for, d < 40 nm, and stable growth for, d >= 40 nm. Interestingly, the growth exponent (beta) is found to be distinctly different, similar to 0.22 and similar to 0.90, for the films on ITO and SiO2 substrates, respectively. The study of the temperature-dependent growth kinetics yields higher activation energy (E-a) for SiO2 (similar to 0.15 eV) than that of ITO (similar to 0.10 eV). Due to mound-like growth, the film on SiO2 substrate deviates from the conventional scaling law. Structural and photoluminescence (PL) studies reveal better crystallinity of the film on ITO, which is consistent with its low E-a value. Optical absorbance and PL analyses reveal a blue shift in the bandgap with decreasing thickness attributed to the lattice expansion. These findings provide new insights on the growth kinetics and optimum conditions for the vacuum deposition of hybrid perovskite thin films on various substrates.

Herein, we demonstrate the room temperature growth of ultra-small perovskite quantum dots (QDs) on a mesoporous TiO2 template fabricated via a low temperature solvothermal route. FESEM image of pristine TiO2 template reveals various exposed facets, which are relatively smooth. Rapid thermal annealing (RTA) under vacuum transforms the template into highly porous TiO2 mesostructure. TEM images reveal uniform growth of perovskite QDs on the TiO2 templates. Size of perovskite QDs grown on RTA treated template (similar to 2 nm) is much smaller than that of furnace annealed template. Interestingly, the size of the as-grown perovskite QDs is fully consistent with the pore size of templates. CH3NH3PbBr3 QDs grown on RTA treated template exhibits similar to 72 fold enhancement in PL intensity as compared to bulk Br3 film and similar to 13 fold enhanced photoluminescence (PL) intensity as compared to that of non-RTA treated template. Similarly, CH3NH3PbI3 QDs exhibits similar to 26 fold enhanced PL compared to bulk I3 film, and the PL peak is observed to be blue shifted by 13 nm as compared to that grown without RTA treatment. The absorption edge of perovskite QDs grown on RTA treated template is observed to be blue shifted. Our analysis reveals that due to the smaller size and high density of pores, perovskite QDs encaged in the TiO2 mesopores experience strong quantum confinement effect, resulting in the strong enhancement of PL intensity along with the blue shift of absorption edge/ PL peak caused by the band gap enlargement.

Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large exciton binding energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7-5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV-visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size similar to 1.7 nm exhibits similar to 47 nm blue shift in the PL spectra, similar to 43 fold enhancement in PL intensity and similar to 25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (similar to 124 times) PL emission with narrow line width and a PLQY of similar to 57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high exciton binding energy (162-272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (>= 10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to <67%. Thus, template grown hybrid perovskite QDs exhibiting high photostability and very high PLQY demonstrated here are promising for the next generation optoelectronic applications. (C) 2018 Elsevier Inc. All rights reserved.

Human fungal diseases pose a significant danger, but often overlooked, burden on public health, affecting over 1 billion people worldwide. Superficial fungal infections (e.g. nail, skin and urogenital) affect most people at some point in their lifetimes, but are usually curable when treated with antifungal drugs. Nevertheless, they affect quality of life and burden health services. Transdermal drug delivery is one of the promising drug delivery system for administration of drug across the skin but it has drawback of less permeability due to the stratum corneum, the outer most protective layer which prohibit the entry of xenobiotics. Therefore several vesicular drug delivery systems have been developed. The present aim of the study is to increase the permeability of Bifonazole which is a broad spectrum antifungal imidazole drug. It is a class iv drug which has less permeability and low solubility, so as to increase the permeability and solubility, it has been loaded into one of the best vesicular system i.e. transferosomes which has ultradeformable flexibility. In this study 12 formulations were prepared by reverse phase evaporation method using soya lecithin, span60, span 80 and tween 80 and evaluated for in vitro drug release. Five formulations for each surfactant were prepared by keeping the drug concentration constant. Among three surfactants span 60 showed better results. Among the five formulations of span 60, F1 and F2 with ratio of 2:1 and 4:1 of soya lecithin and span 60 respectively showed highest drug release of 75.905% and 94.8% respectively. F2 showed highest drug content and entrapment efficiency of 91.25 and 93.13%.But zeta potential report showed very low stability; hence to increase the stability of formulation; cholesterol was added in the ratio of 2:1 and 4:1 of phospholipid and cholesterol respectively. Then the zeta potential results of formulation were in the acceptable range. Hence it can be concluded that Bifonazole can be loaded in to transferosomal carrier which was found to be effective for increasing the permeability and can be proceeded for further future studies.