Printing strategies for scaling-up perovskite solar cells

Photovoltaic technology offers a sustainable solution to the problem of soaring global energy demands. Recently, metal halide perovskite solar cells (PSCs) have attracted worldwide interest because of their high power conversion efficiency of 25.5% and great potential in becoming a disruptive technology in the photovoltaic industry. The transition from research to commercialization requires advancements of scalable deposition methods for both perovskite and charge transporting thin films. Herein, we share our view regarding the current challenges to fabrication of PSCs by printing techniques. We focus particularly on ink technologies, and summarize the strategies for printing uniform, pinhole-free perovskite films with good crystallinity. Moreover, the stability of perovskite solar modules is discussed and analyzed. We believe this review will be advantageous in the area of printable electronic devices.     

Rational design of high-quality 2D/3D perovskite heterostructure crystals for record-performance polarization-sensitive photodetection

Polarization-sensitive photodetection is central to optics applications and has been successfully demonstrated in photodetectors of two-dimensional (2D) materials, such as layered hybrid perovskites; however, achieving high polarization sensitivity in such a photodetector remains extremely challenging. Here, for the first time, we demonstrate a high-performance polarization-sensitive photodetector using single-crystalline 2D/3D perovskite heterostructure, namely, (4-AMP)(MA)₂Pb₃Br₁₀/MAPbBr₃ (MA = methylammonium; 4-AMP = 4-(aminomethyl)piperidinium), which exhibits ultrahigh polarization sensitivity up to 17.6 under self-driven mode. To our knowledge, such a high polarization selectivity has surpassed all of the reported perovskite-based devices, and is comparable to, or even better than, the traditional inorganic heterostructure-based photodetectors. Further studies reveal that the built-in electric field formed at the junction can spatially separate the photogenerated electrons and holes, reducing their recombination rate and thus enhancing the performance for polarization-sensitive photodetection. This work provides a new source of polarization-sensitive materials and insights into designing novel optoelectronic devices.     

Regulating off-centering distortion maximizes photoluminescence in halide perovskites

Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH₃NH₃GeI₃, HC(NH₂)₂GeI₃, and CsGeI₃]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH₃NH₃⁺ with Cs⁺ to control the distortion in (CH₃NH₃)_1-xCs_xGeI₃, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI₃ further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods.     

基于成员决策柔性的知识联盟不稳定性研究

知识联盟的本质是一种战略联盟,也是企业获取知识的重要方式。但现实中普遍存在的战略联盟不稳定现象受到越来越多的关注。在考虑成员决策柔性和联盟收益不确定的情况下,通过构建定量分析模型,对联盟的不稳定性进行了分析研究,重点是对联盟成员退出联盟的条件及时机进行分析和研究。结果表明,成员企业基于决策柔性的等待行为及收益不确定性的加大会促进联盟的稳定;而由于联盟契约的不完全性所导致的专用性投资不足,则会导致联盟的不稳定。     

椎间盘软骨终板的退变机理及相关实验研究概述

椎间盘退变是颈椎病、椎体失稳、椎体滑脱、椎间盘突出等脊柱疾病的重要病因,而软骨终板与椎间盘退变关系密切,研究已经证明,椎间盘的退变最早是从软骨终板开始,软骨终板的退变也是加速椎间盘退变的一个重要原因。近年来有关软骨终板的退变机理的研究日渐增多,通过这些研究,可以对软骨终板在椎间盘退变性疾病中的病变机制和作用有进一步的认识,为椎问盘退变的早期预防和治疗开辟一条新的道路。     

非线性计算不稳定问题的进一步研究

讨论了有关非线性计算不稳定的若干问题,其主要内容有(1)考察了有代表性的三类发展方程,指出其对应的差分格式是否出现非线性计算不稳定,与原微分方程解的性质密切相关;(2)进一步讨论了带周期边条件的守恒型差分格式的非线性计算稳定性问题,总结了克服非线性不稳定的有效措施;(3)以非线性平流方程为例,着重分析了带非周期边条件的非守恒差分格式的非线性计算稳定性问题,给出了判别其计算稳定性的"综合分析判别法".     

A multiaxial lead-free two-dimensional organic-inorganic perovskite ferroelectric

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) have recently gained tremendous interest because of their unique features in contrast to three-dimensional counterparts and traditional 2D materials. However, although some 2D HOIP ferroelectrics have been achieved, the issue of toxic Pb and uniaxial nature impede their further application. Herein, for the first time, we report a lead-free 2D HOIP multiaxial ferroelectric, [3,3-difluorocyclobutylammonium]₂CuCl₄ (1), which shows four ferroelectric axes and eight equivalent polarization directions, more than those of the other 2D HOIP ferroelectrics and even the inorganic perovskite ferroelectric BaTiO₃ (three ferroelectric axes and six equivalent polarization directions). 1 also features a high Curie temperature of 380 K and exhibits remarkable thermochromism of color change from green-yellow to dark brown. To our knowledge, 1 is the first multiaxial lead-free 2D HOIP ferroelectric. This work sheds light on the exploration of better lead-free 2D HOIP ferroelectrics.     

Anomalous strain effect on the thermal conductivity of low-buckled two-dimensional silicene

The thermal conductivity of two-dimensional materials, such as graphene, typically decreases when tensile strain is applied, which softens their phonon modes. Here, we report an anomalous strain effect on the thermal conductivity of monolayer silicene, a representative low-buckled two-dimensional (LB-2D) material. ReaxFF-based molecular dynamics simulations are performed to show that biaxially stretched monolayer silicene exhibits a remarkable increase in thermal conductivity, by as much as 10 times the freestanding value, with increasing applied strain in the range of [0, 0.1], which is attributed to increased contributions from long-wavelength phonons. A further increase in strain in the range of [0.11, 0.18] results in a plateau of the thermal conductivity in an oscillatory manner, governed by a unique dynamic bonding behavior under extreme loading. This anomalous effect reveals new physical insights into the thermal properties of LB-2D materials and may provide some guidelines for designing heat management and energy conversion devices based on such materials.     

Control over π-π stacking of heteroheptacene-based nonfullerene acceptors for 16% efficiency polymer solar cells

Nonfullerene acceptors are being investigated for use in polymer solar cells (PSCs), with their advantages of extending the absorption range, reducing the energy loss and therefore enhancing the power conversion efficiency (PCE). However, to further boost the PCE, mobilities of these nonfullerene acceptors should be improved. For nonfullerene acceptors, the π–π stacking distance between cofacially stacked molecules significantly affects their mobility. Here, we demonstrate a strategy to increase the mobility of heteroheptacene-based nonfullerene acceptors by reducing their π–π stacking distances via control over the bulkiness of lateral side chains. Incorporation of 2-butyloctyl substituents into the nonfullerene acceptor (M36) leads to an increased mobility with a reduced π–π stacking distance of 3.45 Å. Consequently, M36 affords an enhanced PCE of 16%, which is the highest among all acceptor-donor-acceptor-type nonfullerene acceptors to date. This strategy of control over the bulkiness of side chains on nonfullerene acceptors should aid the development of more efficient PSCs.     

Microfluidics-based devices: New tools for studying cancer and cancer stem cell migration

Cell movement is highly sensitive to stimuli from the extracellular matrix and media. Receptors on the plasma membrane in cells can activate signal transduction pathways that change the mechanical behavior of a cell by reorganizing motion-related organelles. Cancer cells change their migration mechanisms in response to different environments more robustly than noncancer cells. Therefore, therapeutic approaches to immobilize cancer cells via inhibition of the related signal transduction pathways rely on a better understanding of cell migration mechanisms. In recent years, engineers have been working with biologists to apply microfluidics technology to study cell migration. As opposed to conventional cultures on dishes, microfluidics deals with the manipulation of fluids that are geometrically constrained to a submillimeter scale. Such small scales offer a number of advantages including cost effectiveness, low consumption of reagents, high sensitivity, high spatiotemporal resolution, and laminar flow. Therefore, microfluidics has a potential as a new platform to study cell migration. In this review, we summarized recent progress on the application of microfluidics in cancer and other cell migration researches. These studies have enhanced our understanding of cell migration and cancer invasion as well as their responses to subtle variations in their microenvironment. We hope that this review will serve as an interdisciplinary guidance for both biologists and engineers as they further develop the microfluidic toolbox toward applications in cancer research.     

区域间高技术产业协同发展关系稳定性条件研究

为促进区域间高技术产业协同发展持续稳定,本文基于改进Lotka－Volterra模型来研究区域间高技术产业协同发展关系的稳定性条件,并以长株潭区域间高技术产业协同发展为案例进行分析。研究表明：区域间高技术产业协同发展系统存在不稳定、鞍点均衡、长期稳定等多种状态;区域间协同影响系数的乘积小于1,是高技术产业协同发展系统稳定的关键条件。政府部门应针对区域间高技术产业协同发展关系稳定性的不同状态,发挥区域不同优势,制定差异化政策,优化区域间高技术产业专业化分工,为协同发展关系维持稳定,甚至向更高层次演化提供重要指引。     

Redox mediators for high-performance lithium–oxygen batteries

Aprotic lithium–oxygen (Li–O₂) batteries are receiving intense research interest by virtue of their ultra-high theoretical specific energy. However, current Li–O₂ batteries are suffering from severe barriers, such as sluggish reaction kinetics and undesired parasitic reactions. Recently, molecular catalysts, i.e. redox mediators (RMs), have been explored to catalyse the oxygen electrochemistry in Li–O₂ batteries and are regarded as an advanced solution. To fully unlock the capability of Li–O₂ batteries, an in-depth understanding of the catalytic mechanisms of RMs is necessary. In this review, we summarize the working principles of RMs and their selection criteria, highlight the recent significant progress of RMs and discuss the critical scientific and technical challenges on the design of efficient RMs for next-generation Li–O₂ batteries.     

How medical practice evolves: Learning to treat failing hearts with an implantable device

In this article we propose that medical practice evolves as a result of progress along three different pathways: improvement in the ability to develop effective medical technologies, learning in medical practice, and advances in biomedical scientific understanding of disease. The relative importance of these three pathways varies from case to case, and often they interact strongly. More specifically, we argue here that in cases of therapeutic innovation where a new medical technology is involved the advance in medical practice is driven largely by the ability to develop and use effective medical artifacts and the interactive sequence among these interdependent pathways often starts with what is learned in practice and not in science. While we state this argument in general, we develop it in detail in a longitudinal and contextual case study of the emergence and evolution of a treatment for advanced heart failure based on an implantable device, the Left Ventricular Assist Device (LVAD). Our findings show that an essential aspect of the evolution of the LVAD therapy is collective and cumulative learning that requires experience that only can be gained through the actual use of LVADs. We discuss the theoretical and policy implications that follow from our understanding of how medical practice evolves for research on the evolution of medical practices and new medical technologies, and policies about the evaluation of rapidly moving medical practices and clinical research involved in their advancement.     

Limitations of autopilot design for controlling a statically unstable flexible interceptor

The Mach number, angle of attack and altitude of operation for an interceptor vary widely during the course of its trajectory. As a result, the interceptor Center of Pressure (CP) locations move significantly around a given Center of Gravity (CG) location at these operating conditions. This results in an inevitable variation in aerodynamic static stability leading to stable and unstable operating regions. In order to ensure good speed of response during the interceptor homing phase, lesser static stability is desirable. Hence the requirement to handle aerodynamic instability at some other operating conditions in the interceptor envelope become inevitable. Since flexibility has a strong bearing on autopilot design, it becomes necessary to control unstable operating points in the presence of flexibility modes. Despite the static stability variation, aerodynamic design can control the level of maximum instability of the configuration. Hence the maximum static instability the autopilot can handle has to be specified for aerodynamic configuration design. This paper brings out the limitations of autopilot design in controlling an unstable interceptor with low bending mode frequencies in terms of maximum instability the autopilot design can handle, which serves as an important input for aerodynamic design.     

设立国家高新区能否促进地区技术进步？——基于生产性服务业集聚视角的机制检验

本文以生产性服务业集聚为切入点,运用双重差分法考察了设立国家高新区的技术进步效应。研究发现：（1）国家高新区的设立并未显著带动地区技术进步;（2）出现上述现象的原因在于设立国家高新区显著吸引了低端生产性服务业集聚,但并未吸引对技术进步具有积极影响的高端生产性服务业在区域内形成集聚;（3）进一步分析发现,发挥“成本效应”和“生产率效应”是吸引高端生产性服务业入区、促进地区技术进步的有效途径,且“成本效应”中制造业发展、“生产率效应”中创新人才积累是最为有效的两种途径。     

Entrepreneurial experiments in science policy: Analyzing the Human Genome Project

We re-conceptualize the role of science policy makers, envisioning and illustrating their move from being simple investors in scientific projects to entrepreneurs who create the conditions for entrepreneurial experiments and initiate them. We argue that reframing science policy around the notion of conducting entrepreneurial experiments - experiments that increase the diversity of technical, organizational and institutional arrangements in which scientific research is conducted - can provide policy makers with a wider repertoire of effective interventions. To illustrate the power of this approach, we analyze the Human Genome Project (HGP) as a set of successful, entrepreneurial experiments in organizational and institutional innovation. While not designed as such, the HGP was an experiment in funding a science project across a variety of organizational settings, including seven public and one private (Celera) research centers. We assess the major characteristics and differences between these organizational choices, using a mix of qualitative and econometric analyses to examine their impact on scientific progress. The planning and direction of the Human Genome Project show that policy makers can use the levers of entrepreneurial experimentation to transform scientific progress, much as entrepreneurs have transformed economic progress.     

Trinucleotide repeats and neuropsychiatric disorders

Expansions of trinucleotide repeats at the level of genomic DNA are increasingly recognized as a cause of a number of neuropsychiatric disorders. Triplet repeat disorders are commonly classified into two groups, those with moderate CAG expansions that result in a polyglutamine stretch in the gene products and those with very long expansions, usually non-CAG, that are not translated. The triplet repeat intergeneration and intra-generational instability, and genetic anticipation characterize disorders. Most of the diseases caused by expanded CAG repeat share common features, which include neurodegeneration, a dominant pattern of inheritance and widespread expression of the gene products with neuronal loss restricted to distinct subset of neurons. Neurodegenerative changes associated of CAG expansion disorders is explained in terms of intra and extra cellular aggregation of mutant gene products, the insoluble nature of the protein(s) being attributed to the presence of polyglutamine stretches, hence their neurotoxic effects. methods based on poymerase chain reaction have become handy in the diagnosis of these genetic disorders. Progress in transgenic animal models for these disorders will be critical for understanding the progress of these disorders and for testing new therapeutic strategies.     

技术批判视野下的现代性问题探究——安德鲁·费恩伯格的“可选择的现代性”理论分析

从对“现代性”的问题诊断和出路探究两方面分析了美国技术哲学家安德鲁·费恩伯格的“可选择的现代性”理论。对“现代性”的“问题”诊断包括理性的分化导致现代人对理性内涵的理解过于狭窄、对技术的本质和判断“进步”的标准等问题的理解上出现偏差等三个方面,进而阐述了对“现代性”出路的思考,即现代性的特征是由文化决定的,不同区域的文化形成了不同的技术,进而形成了各具特色的现代性,文化通过具体化的方式选择技术,其结果是文化和技术的相容性,最后对这一理论作了评析,提出“可选择的现代性”理论的实质是对传统文化与现代性关系问题的探讨。     

Dependency-based IT Governance practices in inter-organisational collaborations: A graph-driven elaboration

In an ever more globalised world IT (Information Technology) managers increasingly have to support value creation within inter-organisational collaboration settings. Such organisational forms with their inherent complexity require specific approaches for their IT management within. Especially important for unleashing the chances of networked arrangements is the right form of IT Governance. Choosing the right arrangement for IT Governance is heavily dependent on understanding the concepts on which such business constellations are built. In this paper we provide therefore first a systematically derived, graph-based perspective on the key terms of inter-organisational collaboration. Based on this understanding of concepts and structured representations of inter-organisational dependencies we present interorganisational governance practices for IT. Specifically, we assign accountabilities to top executive roles from both IT and business. By keeping a holistic perspective, the insights gained in this study are highly relevant for strategic information management in terms of Business-IT Alignment as well as monitoring and controlling of inter-organisational information infrastructures in a rapidly changing business environment.