Electron beam microscopy and related characterization techniques play an important role in revealing the microstructural, morphological, physical, and chemical information of halide perovskites and their impact on associated optoelectronic devices. However, electron beam irradiation usually causes damage to these beam-sensitive materials, negatively impacting their device performance, and complicating this interpretation. In this article, the electron microscopy and spectroscopy techniques are reviewed that are crucial for the understanding of the crystallization and microstructure of halide perovskites (e.g. MAPbI 3 , CsPbBr 3 ). In addition, special attention is paid to assessing and mitigating the electron beam-induced damage caused by these techniques during measurements of both organic-inorganic hybrid and all-inorganic halide perovskites. Since the halide perovskites are fragile, a protocol involving delicate control of both electron beam dose and dose rate, coupled with careful data analysis, is shown to be the key to enable the acquisition of reliable structural and compositional information such as atomic-resolution images, chemical elemental mapping and electron diffraction patterns. Limiting the electron beam dose is shown to be the critical parameter enabling the characterization of various halide perovskite materials. Novel methods to unveil the mechanisms of device operation, including charge carrier generation, diffusion, and extraction are presented in scanning electron microscopy studies combined with electron-beam induced current and cathodoluminescence mapping. Future opportunities for electron-beam related characterizations of halide perovskites are also discussed.

A significant challenge facing perovskite narrowband photodetectors is making high-quality and thick enough films. Here, we report a facile one-step spray-coating approach to deposit cesium lead halide perovskite thick films for filterless narrowband photodetectors, which exhibited a specific detectivity of 2.43 × 1010 Jones at 655 nm with an fwhm of 25 nm. We demonstrated that both substrate temperature and deposition time during the spray-coating process are key factors that govern the thickness and morphology of perovskite films. The photodetection behavior was dependent on the film thickness, and the narrowband photoresponse was recorded at a 3.9 μm thickness. We discovered that the internal electric field also plays a critical role in determining the narrowband photoresponse behavior. A distinct photoresponse behavior was observed when respectively applying a reverse bias and a forward bias, which is ascribed to the trade-off between the charge-trapping effect and charge extraction under the internal built-in electric field in different biased conditions. Through changing the halogen composition of perovskites from CsPbCl2Br to CsPbI2Br, the peak position of the narrowband spectral photoresponse was observed to shift from 460 to 660 nm. This study not only offers a controllable spray-coating approach to develop thick perovskite films but also provides an important guidance for the rational design of filterless narrowband photodetectors for practical applications in industrial control, visual imaging, and biological sensing.

Organometal halide perovskites as the core of the next-generational photovoltaic technologies have attracted remarkable attention due to their advantages of low material cost, easy fabrication, and outstanding photovoltaic properties. [1] Significant efforts have been made to enhance the photovoltaic performance of perovskite solar cells (PSCs). [2] The power conversion efficiency (PCE) has been boosted to about 26%, [3] which is comparable to that of conventional photovoltaic technology based on crystalline silicon. Nevertheless, the device instability suffering from moisture exposure and heat attack is still a significant barrier on the road toward commercialization. [4] It is known that halide perovskites with low formation energy are intrinsically unstable so that they are easy to deteriorate under various external forces. [5] Therefore, how to stabilize the perovskite structure and films is the most important concern in the PSCs.Recently, several effective strategies, including interfacial engineering, additive engineering, dimensional manipulation, and so on, have been applied to improve device stability. [6] Caffeine (1,3,7-trimethylxanthine) was employed as an additive to increase the activation energy of perovskite films through a molecular lock between carboxyl groups and bivalent Pb, yielding PSCs with good thermal stability at 85 C. [7] Lin et al. proved that the introduction of a piperidinium salt into the perovskites could slow down degradation of the perovskite layer under continuous illumination. [8] Additionally, by depositing n-hexyl trimethyl ammonium bromide on the top of the perovskite film, a thin layer of wide-bandgap halide perovskites was formed through an in situ reaction, leading to a high efficiency of 22.7% and good stability both at 85% relative humidity and under one-sun illumination. [9] Despite these progresses, few studies have considered crystallization control of the halide perovskites, which could be a critical approach to concurrently improve both PCE and device stability. Given that the nucleation and crystallization of perovskites during both initial spin-coating and subsequent annealing process are correlated with the PbI 2 precursor solution, [10,11] it is necessary to tune crystallization of perovskite by coordinating the precursor solution to enhance chemical bonding interactions to deliver high-quality and stable perovskite films.

Energy loss induced by nonradiative recombinations plays a critical role in determining power conversion efficiencies in perovskite solar cells, whereas device stability impacts their long‐time reliability in the ambient environment. It is an important challenge to suppress energy loss and improve device stability simultaneously. Herein, an interfacial layer of triphenylamine (TPA):polystyrene (PS) blend coated on the hybrid perovskite layer to concurrently suppress energy loss and improve device stability is reported. The energy loss is suppressed from 0.49 to 0.35 eV by passivating surface defects in hybrid perovskites via Lewis acid–base interactions with the combination of electron‐donating aromatic nucleus in PS and tertiary amine in TPA, leading to perovskite solar cells with a high open‐circuit voltage of 1.18 V, a fill factor of about 80%, and a power conversion efficiency of 22.1%. Meanwhile, the device stability in the ambient environment is improved significantly by the TPA:PS blend due to its superior hydrophobicity which is suggested by its high contact angle of 91.1° as compared to 64.0° for the pristine perovskite film. Herein, an efficient interfacial engineering approach with the TPA:PS blend to suppress energy loss and improve device stability simultaneously towards realistic applications is demonstrated.

Two kinds of POPs were synthesized with unique porous structures, considerable specific surface areas and high adsorption capacities. The specific surface area and pore diameter could be adjusted via changing the reaction time and temperature.

Glucose biosensors play a critical role in clinically examining the blood sugar level to assess whether the pancreas performs normally to release insulin. However, the sensitivity of state‐of‐the‐art glucose biosensors is still insufficient to ensure a reliable non‐invasive examination of blood sugar level in the low‐concentration glucose‐containing‐samples such as interstitial fluids, perspiration, and saliva. Here, a facile method is reported on to improve glucose sensitivity of electrochemical reaction based biosensors by modifying the electrode with building blocks of ion‐sputtering‐coated 3.4 nm gold (Au) nanoparticles. High‐resolution transmission electron microscopy studies in combination with electrochemical characterizations reveal that the improvement of glucose biosensor performance resulted from better charge transfer during the electrochemical reaction process, which is attributed to the modification of electrodes with catalytically active Au nanoparticles. The glucose sensitivity is demonstrated to be more than doubled in the flexible glucose biosensors with the modification of various electrodes (e.g., Au, conductive carbon). The Au‐electrode‐based glucose biosensors after modification with Au nanoparticles yield a sensitivity of 216.9 µA mm−1 along with a detection limit of 1 × 10–6 m. This study paves a practicable way to develop more sensitive glucose biosensors by the modification of electrodes with building blocks of Au nanoparticles toward non‐invasive blood‐glucose monitoring applications.

The performance of perovskite photodetectors was often tuned by changing the functional groups of polymeric additives, rather than their molecular weight to improve defect passivation. As a result of the steric effect of polymeric additives, we found that the molecular weight of poly(ethylene glycol) (PEG) additives played an important role in determining the perovskite crystal size, which increased from 470 to 550 nm with increasing molecular weight from 6k to 10k but declined back to 450 nm with further increasing molecular weight to 20k. The noise current, rather than the external quantum efficiency, was the dominant factor that can be tailored to improve the photodetection performance using PEG additives with different molecular weights. The photodetectors based on the 10k PEG additive exhibited a high specific detectivity of 1.9 × 10 11 Jones, a linear dynamic range of 119 dB, and a frequency response −3 dB of 11.57 kHz. This work demonstrates an alternative approach by tailoring the molecular weight of polymeric additives to optimize the morphology of perovskite films for improved performance in perovskite photodetectors and other perovskite optoelectronic devices.

Fluorescent chemosensors based on silica nanoparticles and silicate glass slides were well designed and prepared. The as-prepared fluorescent silica particles and glass slides exhibited highly selective sensing and absorbing abilities to Pd 2? ions in aqueous phase. SiO 2 nanoparticles were first synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS), and then -NH 2 groups were introduced to silica by treating with 3-aminopropyltriethoxysilane (APTES). Subsequently, 4-amino-1,8-naphthalic anhydride (ANA) was incorporated with the reaction of -NH 2 groups. Finally, salicylaldehyde (SA) was introduced by the reaction between amino groups in ANA and the -CHO groups in SA. Thus, the fluorescent silica nanoparticles were obtained. This method was expanded to prepare fluorescent silicate glass slides. Upon the addition of Pd 2? ions, the fluorescence quenched immediately. These chemosensors were selectively sensitive to Pd 2? ions as low as 10 lM. The absorption efficiency of fluorescent nanoparticles and glass slides for Pd 2? reached to 38.38 and 27.50 %, respectively. And the chemosensors also could be easily recycled and reused for at least five times. Fluorescent silica nanoparticles with only ANA or SA (not ANA and SA together) also exhibited the sensing ability to Pd 2? ions; however, it showed the shortage of Pd 2? ions selectivity. It suggested that it is necessary to introduce both ANA and SA for the high sensitivity and selectivity to Pd 2? ions.