The trap states at grain boundaries (GBs) within polycrystalline perovskite films deteriorate their optoelectronic properties, making GB engineering particularly important for stable high-performance optoelectronic devices. It is demonstrated that trap states within bulk films can be effectively passivated by semiconducting molecules with Lewis acid or base functional groups. The perovskite crystallization kinetics are studied using in situ synchrotron-based grazing-incidence X-ray scattering to explore the film formation mechanism. A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb-I antisite defects and vacancies created by under-coordinated Pb atoms. In addition, it also explains how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport. The superior optoelectronic properties are attained by optimizing the molecular passivation treatments. These benefits are translated into significant enhancements of the power conversion efficiencies to 19.3%, as well as improved environmental and thermal stability of solar cells. The passivated devices without encapsulation degrade only by ≈13% after 40 d of exposure in 50% relative humidity at room temperature, and only ≈10% after 24 h at 80 °C in controlled environment.
In a recent letter (J. Phys. Chem. A, 2001, 105,1), we argued that, although all major thermochemical tables recommend a value of ∆H°f 0 (OH) based on a spectroscopic approach, the correct value is 0.5 kcal/mol lower as determined from an ion cycle. In this paper, we expand upon and augment both the experimental and theoretical arguments presented in the letter. In particular, three separate experiments (mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photoelectron-photoion coincidence measurements) utilizing the positive ion cycle to derive the O-H bond energy are shown to converge to a consensus value of the appearance energy AE 0 (OH(18.116 2 ( 0.003 0 eV). With the most accurate currently available zero kinetic energy photoionization value for the ionization energy IE(OH) ) 104989 ( 2 cm -1 , corroborated by a number of photoelectron measurements, this leads to D 0 (H-OH) ) 41128 ( 24 cm -1 ) 117.59 ( 0.07 kcal/mol. This corresponds to ∆H f0 (OH) ) 8.85 ( 0.07 kcal/mol and implies D 0 (OH) ) 35593 ( 24 cm -1 ) 101.76 ( 0.07 kcal/mol. These results are completely supported by the most sophisticated theoretical calculations ever performed on the H x O system, CCSD(T)/aug-cc-pVnZ, n ) Q, 5, 6, and 7, extrapolated to the CBS limit and including corrections for core-valence effects, scalar relativistic effects, incomplete correlation recovery, and diagonal Born-Oppenheimer corrections. These calculations have an estimated theoretical error of e0.2 kcal/mol based on basis set convergence properties. They reproduce the experimental results for dissociation energies, atomization energies, and ionization energies for the H x O system to within 0.0-0.2 kcal/mol. In contrast, the previously accepted values of the two successive bond dissociation energies of water differ from the current values by 0.5 kcal/mol. These values were derived from the spectroscopic determinations of D 0 (OH) using a very short Birge-Sponer extrapolation on OH/OD A 1 Σ + . However, on the basis of a calculation of the A state potential energy curve (with a multireference single and double excitation wave function and an augcc-pV5Z basis set) and an exhaustive reanalyzis of the original measured data on both the A and B states of OH, the Birge-Sponer extrapolation can be demonstrated to significantly underestimate the bond dissociation energy, although only the last vibrational level was not observed experimentally. The recommended values of this paper affect a large number of other thermochemical quantities which directly or indirectly rely on or refer to D 0 (H-OH), D 0 (OH), or ∆H°f(OH). This is illustrated by an analysis of several reaction enthalpies, deprotonation enthalpies, and proton affinities.
China's Loess Plateau is both the largest and deepest loess deposit in the world, and it has long been one of the most severely eroded areas on Earth. Since the 1970s, numerous soil- and water-conservation practices have been implemented: terracing, planting of vegetation, natural vegetation rehabilitation, and check-dam construction. With the implementation of the Grain-for-Green Project in 1999, the Loess Plateau has become the most successful ecological restoration zone in China. However, these large-scale restoration measures and drought have significantly reduced both runoff and sediment from the Loess Plateau. This situation has both advantages and disadvantages for the lower Yellow River. Some local soil erosion has been successfully controlled, but the whole regional ecosystem remains very fragile. Therefore, it is necessary to balance each ecosystem service, for example, by determining the region's vegetation capacity and its spatial distribution for the sustainable development of the socioecological system of the Loess Plateau.
Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA) (MA) Pb I phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA) (MA) Pb I films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices.
13The new decade of the 21 st century (2020) started with the emergence of novel 14 coronavirus known as SARS-CoV-2 that caused an epidemic of coronavirus disease in Wuhan, China. It is the third highly pathogenic and transmissible coronavirus after severe 16 acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome 17 coronavirus (MERS-CoV) emerged in humans. The source of origin, transmission to humans and 18 mechanisms associated with the pathogenicity of SARS-CoV-2 are not clear yet, however, its 19 resemblance with SARS-CoV and several other bat coronaviruses was recently confirmed 20 through genome sequencing related studies. The development of therapeutic strategies is 21 necessary in order to prevent further epidemics and cure infected people. In this Review, we 22 summarize current information about the emergence, origin, diversity, and epidemiology of three 23 pathogenic coronaviruses with a specific focus on the current outbreak in Wuhan, China. 24 Furthermore, we discuss the clinical features and potential therapeutic options that may be 25 effective against SARS-CoV-2. 26
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