Metal‐halide perovskites (MHPs) are regarded as ideal photovoltaic materials because of their variable crystal material composition and superb optoelectronic performance. However, this compositional ...variability results in a complicated crystallization process during MHP film fabrication, leading to reduced MHP film crystallinity and decreased performance of devices containing such films. The crystallization kinetics of MHPs have therefore been extensively explored in efforts to determine the effect of crystallization properties on MHP film properties and figure out the corresponding modulating strategies. Here, the first comprehensive review of reported studies on the crystallization properties of 3D MHPs is presented. The experimental and theoretical research on 3D MHP crystallization kinetics is systematically surveyed, and the methods that are used for modulating MHP crystallization are summarized, namely, solution engineering, compositional engineering, interfacial engineering, and additive passivation. Meanwhile, the prospects and current challenges in revealing perovskite crystallization kinetics are suggested.
The vast literature on experimental and theoretical research on the nucleation and growth of metal‐halide perovskite films, as well as the relationships between film properties and crystallization modulating methods including solution engineering, composition engineering, interface engineering, and additive passivation are systematically reviewed. This work consolidates the research on metal‐halide perovskite crystallization kinetics, and highlights new and promising areas of study.
Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. ...However, an in‐depth understanding of the organic‐spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy‐level alignments at the 2D/3D interfaces and therefore influence the charge‐transfer characteristics. The strong intermolecular interactions between the 2,2‐(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic PbI64− slabs facilitate a controlled deposition of a phase‐pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE‐based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer‐chemistry design for high‐performance 2D/3D PSCs.
Herein, three iodized diammonium spacers are selected to study the effects of chain length and heteroatom incorporation on the related interfacial properties of 2D/3D perovskite heterostructures. The structure tailoring and concentration control of organic spacers contribute to the well‐controlled phase purity, improved quantum well orientation, and energetic band alignment at 2D/3D interfaces, and thus enhanced device efficiency.
Monolithic perovskite/organic tandem solar cells have attracted increasing attention due to their potential of being highly efficient while compatible to facile solution fabrication processes. One of ...the limiting factors for improving the performance of perovskite/organic tandem cells is the lack of wide‐bandgap perovskites with suitable bandgap, film quality, and optoelectronic properties for front cells. In addition, the development of low‐bandgap organic bulk‐heterojunction (BHJ) rare cells with extended absorption in the infrared range is also critical for improving tandem cells. This work has carefully optimized mixed halide wide‐bandgap perovskite (MWP) films by introducing a small amount of formamidinium (FA+) cations into the basic composition of MA1.06PbI2Br(SCN)0.12, which provides an effective means to modulate the crystallization properties and phase stability of the films. At optimized conditions, the MA0.96FA0.1PbI2Br(SCN)0.12 forms high‐quality films with grain boundaries homogeneously passivated by PbI2, leading to a reduction in defect states and an enhancement in phase stability, enabling the fabrication of perovskite solar cells with a power conversion efficiency(PCE) of 17.4%. By further integrating the MWP front cell with an organic BHJ (PM6:CH1007) rare cell composed of a nonfullerene acceptor with absorption extended to 950 nm, a tandem cell with PCE over 21% is achieved.
The effect of formamidinium (FA+) on modulating methylammonium (MA+) based (mixed‐halide wide‐bandgap preovskites) MWPs (MA1.06PbI2Br(SCN)0.12) crystallization properties for achieving high‐quality perovskite films is evaluated. Based on the optimized MA0.96FA0.1PbI2Br(SCN)0.12 film, a monolithic perovskite/organic tandem solar cells with a new record high‐efficiency of 21.2% is achieved.
Passivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. ...Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI3 perovskite films as evidenced by photothermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical‐field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to −2 V reverse voltage bias which is much larger than the breakdown voltage of −0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.
Polymer additives in perovskite solar cells are found to act as barriers at the perovskite grain boundaries and hinder the ion migration, improving the device stability under both light irradiation and electrical stressing. The polymer incorporated perovskite solar cells have significantly increased electrical‐field tolerance with an increase in breakdown voltage from −0.4 to −2 V.
The ever‐growing need to inspect matter with hyperfine structures requires a revolution in current scintillation detectors, and the innovation of scintillators is revived with luminescent metal ...halides entering the scene. Notably, for any scintillator, two fundamental issues arise: Which kind of material is suitable and in what form should the material exist? The answer to the former question involves the sequence of certain atoms into specific crystal structures that facilitate the conversion of X‐ray into light, whereas the answer to the latter involves assembling these crystallites into particular material forms that can guide light propagation toward its corresponding pixel detector. Despite their equal importance, efforts are overwhelmingly devoted to improving the X‐ray‐to‐light conversion, while the material‐form‐associated light propagation, which determines the optical signal collected for X‐ray imaging, is largely overlooked. This perspective critically correlates the reported spatial resolution with the light‐propagation behavior in each form of metal halides, combing the designing rules for their future development.
This perspective considers light propagation in metal halide scintillators as the focus. By correlating the reported spatial resolution with light propagation in various forms, this perspective clarifies and deepens the understanding of untouched yet fundamental issues, namely, material‐form‐associated light propagation in metal halide scintillators, and provides the design rules for their future development.
Cephalodiones A–D (1–4), the first example of C19‐norditerpenoid dimers, were isolated and fully characterized from a Cephalotaxus plant. These new skeletal natural products shared a unique ...tricyclo6.4.1.12,7tetradeca‐3,5,9,11‐tetraene‐13,14‐dione core that was capped in both ends with rigid multicyclic ring systems either C2‐symmetrically or asymmetrically. Compounds 1–4 were proposed to be biosynthetically produced by the 6+6‐cycloaddition of two identical C19‐norditerpenoid troponoids, which was validated by the semisyntheses of dimers 2–4. Moreover, some compounds showed significant inhibition on Th17 cell differentiation.
Chemical study on a Cephalotaxus plant led to the characterization of four unprecedented C19‐norditerpenoid dimers, named cephalodiones A–D (1–4). These compounds were proposed to be biosynthetically formed through 6+6‐cycloaddition of two C19‐norditerpenoid troponoids either C2‐symmetrically or asymmetrically, which was validated by the semisyntheses of 2–4. Some compounds showed significant inhibition on Th17 cell differentiation.
Purpose
Segmentation of pulmonary nodules is critical for the analysis of nodules and lung cancer diagnosis. We present a novel framework of segmentation for various types of nodules using ...convolutional neural networks (CNNs).
Methods
The proposed framework is composed of two major parts. The first part is to increase the variety of samples and build a more balanced dataset. A conditional generative adversarial network (cGAN) is employed to produce synthetic CT images. Semantic labels are generated to impart spatial contextual knowledge to the network. Nine attribute scoring labels are combined as well to preserve nodule features. To refine the realism of synthesized samples, reconstruction error loss is introduced into cGAN. The second part is to train a nodule segmentation network on the extended dataset. We build a three‐dimensional (3D) CNN model that exploits heterogeneous maps including edge maps and local binary pattern maps. The incorporation of these maps informs the model of texture patterns and boundary information of nodules, which assists high‐level feature learning for segmentation. Residual unit, which learns to reduce residual error, is adopted to accelerate training and improve accuracy.
Results
Validation on LIDC‐IDRI dataset demonstrates that the generated samples are realistic. The mean squared error and average cosine similarity between real and synthesized samples are 1.55×10−2 and 0.9534, respectively. The Dice coefficient, positive predicted value, sensitivity, and accuracy are, respectively, 0.8483, 0.8895, 0.8511, and 0.9904 for the segmentation results.
Conclusions
The proposed 3D CNN segmentation framework, based on the use of synthesized samples and multiple maps with residual learning, achieves more accurate nodule segmentation compared to existing state‐of‐the‐art methods. The proposed CT image synthesis method can not only output samples close to real images but also allow for stochastic variation in image diversity.
The strained cyclopropane and/or cyclobutane subunits occurred in many complex natural products including terpenoids, steroids and alkaloids. Natural products with cyclopropane and/or cyclobutane ...motifs not only furnished fascinating structures, but also exhibited versatile biological activities, such as cytotoxic, anti-HIM antimicrobial, antiviral, and immunosuppressive effects. This review covered a large array of structurally unique natural products with strained cyclopropane and/or cyclobutane motifs and summarized their structural features, distributions, biological activities, as well as biogenetic considerations.
Mixed‐halide wide‐bandgap perovskites are key components for the development of high‐efficiency tandem structured devices. However, mixed‐halide perovskites usually suffer from phase‐impurity and ...high defect density issues, where the causes are still unclear. By using in situ photoluminescence (PL) spectroscopy, it is found that in methylammonium (MA+)‐based mixed‐halide perovskites, MAPb(I0.6Br0.4)3, the halide composition of the spin‐coated perovskite films is preferentially dominated by the bromide ions (Br−). Additional thermal energy is required to initiate the insertion of iodide ions (I−) to achieve the stoichiometric balance. Notably, by incorporating a small amount of formamidinium ions (FA+) in the precursor solution, it can effectively facilitate the I− coordination in the perovskite framework during the spin‐coating and improve the composition homogeneity of the initial small particles. The aggregation of these homogenous small particles is found to be essential to achieve uniform and high‐crystallinity perovskite film with high Br− content. As a result, high‐quality MA0.9FA0.1Pb(I0.6Br0.4)3 perovskite film with a bandgap (Eg) of 1.81 eV is achieved, along with an encouraging power‐conversion‐efficiency of 17.1% and open‐circuit voltage (Voc) of 1.21 V. This work also demonstrates the in situ PL can provide a direct observation of the dynamic of ion coordination during the perovskite crystallization.
By adopting in situ photoluminescence measurement, it is found that the introduction of a small amount of formamidinium ions (FA+) into methylammonium (MA+)‐based mixed‐halide wide‐bandgap perovskites can effectively facilitate I− coordinate into the perovskite framework during the spin‐coating. This method guarantees a MA0.9FA0.1Pb(I0.6Br0.4)3‐based perovskite solar cell with a promising power conversion efficiency of 17.1%.
Two novel pure hydrocarbon compounds, SF33 and SF34, are designed with high triplet energies and stabilities. The efficiency of an SF34/FIrpic‐based device is as high as 22.0%. Moreover, SF33 and ...SF34 are also used as hosts for thermally activated delayed fluorescence organic light‐emitting diodes and achieve external quantum efficiencies in excess of 20.8% and 22.3%, respectively. The pure hydrocarbon host shows a much longer device lifetime than the traditional host 4,4′‐di(N‐carbazolyl)biphenyl.
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