A phase-field model for the evaporation of thin film mixtures

The performance of solution-processed solar cells strongly depends on the geometrical structure and roughness of the photovoltaic layers formed during film drying. During the drying process, the interplay of crystallization and liquid-liquid demixing leads to the structure formation on the nano- and microscale and to the final rough film. In order to better understand how the film structure can be improved by process engineering, we aim at theoretically investigating these systems by means of phase-field simulations. We introduce an evaporation model based on the Cahn-Hilliard equation for the evolution of the fluid concentrations coupled to the Allen-Cahn equation for the liquid-vapour phase transformation. We demonstrate its ability to match the experimentally measured drying kinetics and study the impact of the parameters of our model. Furthermore, the evaporation of solvent blends and solvent-vapour annealing are investigated. The dry film roughness emerges naturally from our set of equations, as illustrated through preliminary simulations of spinodal decomposition and film drying on structured substrates

Phase-field simulation of liquid-vapor equilibrium and evaporation of fluid mixtures

In solution-processing of thin films, the material layer is deposited from a solution composed of several solutes and solvents. The final morphology and hence the properties of the film often depend on the time needed for the evaporation of the solvents. This is typically the case for organic photoactive or electronic layers. Therefore, it is important to be able to predict the evaporation kinetics of such mixtures. We propose here a new phase-field model for the simulation of evaporating fluid mixtures and simulate their evaporation kinetics. Similar to the Hertz-Knudsen theory, the local liquid-vapor equilibrium is assumed to be reached at the film surface and evaporation is driven by diffusion away from this gas layer. In the situation where the evaporation is purely driven by the liquid-vapor equilibrium, the simulations match the behavior expected theoretically from the free energy: for evaporation of pure solvents, the evaporation rate is constant and proportional to the vaporpressure. For mixtures, the evaporation rate is in general strongly time-dependent because of the changing composition of the film. Nevertheless, for highly non-ideal mixtures, such as poorly compatible fluids or polymer solutions, the evaporation rate becomes almost constant in the limit of low Biot numbers. The results of the simulation have been successfully compared to experiments on a polystyrene-toluene mixture. The model allows to take into account deformations of the liquid-vapor interface and therefore to simulate film roughness or dewetting

In Situ Probing the Crystallization Kinetics in Gas‐Quenching‐Assisted Coating of Perovskite Films

The pursuit of commercializing perovskite photovoltaics is driving the development of various scalable perovskite crystallization techniques. Among them, gas quenching is a promising crystallization approach for high‐throughput deposition of perovskite films. However, the perovskite films prepared by gas‐quenching assisted blade coating are susceptible to the formation of pinholes and frequently show inferior crystallinity if the interplay between film coating, film drying, and crystallization kinetics is not fully optimized. That arguably requires a thorough understanding of how single processing steps influence the crystallization kinetics of printed perovskite films. Here, in situ optical spectroscopies are integrated into a doctor‐blading setup that allows to real‐time monitor film formation during the gas‐quenching process. It is found that the essential role of gas quenching treatment is in achieving a smooth and compact perovskite film by controlling the nucleation rate. Moreover, with the assistance of phase‐field simulations, the role of excessive methylammonium iodide is revealed to increase grain size by accelerating the crystal growth rate. These results show a tailored control of crystal growth rate is critical to achieving optimal film quality, leading to fully printed solar cells with a champion power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency are achieved.Utilizing in situ monitoring techniques to optimize the crystallization kinetics of the perovskite films in the gas‐quenching‐assisted blade coating process, a champion power conversion efficiency of 19.50% for a fully printed carbon‐electrode perovskite solar cell is achieved through the tailored control of crystal growth rates. image Bavarian State GovernmentNational Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809Guangzhou Basic and Applied Basic Research FoundationBavarian Ministry of Science and ArtsDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Simplifying contact-layer design for high-throughput printing of flexible perovskite photovoltaics†

The realization of scalable roll-to-roll production processes for metal–halide perovskite modules is a necessary development for transferring developments and technologies from the lab to the fab. Before that, it is imperative to close the efficiency gap not only between the devices fabricated on rigid substrates versus flexible substrates, but also between solar cells to solar modules. In this regard, a critical assessment of device architectures that are more compatible to scalable fabrication is needed. Obviously, the adaption to mass manufacturing must not negatively impact device performance and operational stability. Here, by investigating the properties of printed fullerene-based phosphonic acid dipole interface layers, we establish simplified self-assembled monolayer (SAM) based n–i–p architectures without any charge extraction layers other than SAMs, which are easily processed and are thus ideally suited for mass production. We show that a contact-layer design with a printed fullerene-based SAM that has phosphonic acid is sufficient to provide good charge selectivity and to minimize interface recombination at the bottom electrode. We further show that the same SAM molecule can be used as a p-type interface material on top of the perovskite. This simplified contact-layer design, which is based on one material for both hole and electron work-function adaption is successfully integrated into our fully printed module process comprising the deposition of a carbon top electrode. The achieved open-circuit voltage exceeds 1.1 V, and the fill factor surpasses 70%, highlighting the potential of this novel interface design concept for both rigid and flexible substrates.SAM enabled and simplified fully printed carbon-based flexible perovskite modules.Helmholtz Association 10.13039/501100009318Natural Science Foundation of Jiangsu Province 10.13039/501100004608National Natural Science Foundation of China 10.13039/501100001809Cambridge Trust 10.13039/501100003343Bayerisches Staatsministerium für Bildung und Kultus, Wissenschaft und Kunst 10.13039/501100004563Deutsche Forschungsgemeinschaft 10.13039/501100001659Erlangen Graduate School of Advanced Optical Technologies 10.13039/501100007216China Scholarship Council 10.13039/501100004543Deutscher Akademischer Austauschdienst 10.13039/501100001655Major Basic Research Project of the Natural Science Foundation of the Jiangsu Higher Education Institutions 10.13039/50110001328

Study of high burnup effect on steam oxidation of Zircaloy and its regulatory implications via the developement of a pre-transient oxide model of TRANOX

A mechanisitc model that gives oxygen distribution of Zircaloy cladding with pre-transient oxide and absorbed hydrogen under steam oxidation environments has been developed. The model has been incorporated into TRANOX. The model has been validated against steam oxidation experiments with Zircaloy-4 specimens that were pre-oxidized in simulated PWR environments and past experimental data available in open literature. The high burnup effects on cladding oxidation owing to pre-transient oxide and hydrogen can be categorized into: thinning of initial Zr-matrix by the formation of pre-transient ZrO 2, increasing diffusion resistance of oxygen with pre-transient ZrO2 , and increasing oxygen diffusion rate with a thicker ,beta-phase by ,beta-stabilizing hydrogen. Relative magnitudes of these effects with temperature, pretransient oxide thickness, and hydrogen content determine the dynamics of high burnup fuel oxidation. Mechanistically modeling the high burnup effect, the model comprehensively simulates the integrated effects of pre-transient oxide and absorbed hydrogen. This study confirms that the corrected Cathcart Pawel correlation-based Equivalent Cladding Reacted evaluation method employed by the U.S Nuclear Regulatory Commission is an effective, yet accurate, simplification of the high burnup cladding oxidation modeling for safety analysis of representative LBLOCA of current PWR systems. The application of the developed model to safety analysis revealed allowable discharge burnup limits of 59 and 76 MWd/kgU for Zircaloy-4 and Zr-Nb alloy, respectively from the view point of fuel accident safety. (C) 2022 The Authors. Published by Elsevier B.V.N

Specific Analysis of Web Camera and High Resolution Planetary Imaging

Web camera is usually used for video communication between PC, it has small sensing area, cannot using long exposure application, so that is insufficient for astronomical application. But web camera is suitable for bright planet, moon, it doesn't need long exposure time. So many amateur astronomer using web camera for planetary imaging. We used ToUcam manufactured by Phillips for planetary imaging and Registax commercial program for a video file combining. And then, we are measure a property of web camera, such as linearity, gain that is usually using for analysis of CCD performance. Because of using combine technic selected high quality image from video frame, this method can take higher resolution planetary imaging than one shot image by film, digital camera and CCD. We describe a planetary observing method and a video frame combine method

Upscaling of Perovskite Photovoltaics

Hybrid organic–inorganic perovskite solar cells have reached a certified efficiency of over 25% during the past decade, which has attracted significant attention as a promising candidate for photovoltaics (PVs) applications. However, the most efficient perovskite solar cells were performed by the spin coating technique, which is extremely limited in commercialization. Besides, the efficiencies of large-area perovskite cells and modules are still significantly lower. There are still some challenges that need to overcome to bridge the efficiency gap between small-area perovskite solar cells and large-area perovskite devices. The most important challenge is how to prepare high-quality perovskite layers using cheaper and scalable techniques with high reproducibility. On the other hand, select and deposit charge extraction/transport layers, and the bottom and top electrodes using cheaper and scalable techniques are also important. In this review, recent progress and challenges of the scalable technologies for solution-based coating and printing methods are summarized and analyzed based on the current progress in scalable technologies for solution-based preparation of large-area perovskite PVs. Based on our analysis, we try to point out the major challenges to overcome to successfully bridge the efficiency gap between small-area perovskite solar cells and large-area perovskite devices. Finally, strategies and opportunities are proposed to promote stable and efficient large-area perovskite PVs toward commercialization

Recent progress in strain-engineered elastic platforms for stretchable thin-film devices

Strain-engineered elastic platforms that can efficiently distribute mechanical stress under deformation offer adjustable mechanical compliance for stretchable electronic systems. By fully exploiting strain-free regions that are favourable for fabricating thin-film devices and interconnecting with reliably stretchable conductors, various electronic systems can be integrated onto stretchable platforms with the assistance of strain engineering strategies. Over the last decade, applications of multifunctional stretchable thin-film devices simultaneously exhibiting superior electrical and mechanical performance have been demonstrated, shedding light on the realization of further reliable human-machine interfaces. This review highlights recent developments in enabling technologies for strain-engineered elastic platforms. In particular, representative approaches to realize strain-engineered substrates and stretchable interconnects in island-bridge configurations are introduced from the perspective of the material homogeneity and structural design of the substrate. State-of-the-art achievements in sophisticated stretchable electronic devices on strain-engineered elastic platforms are also presented, such as stretchable sensors, energy devices, thin-film transistors, and displays, and then, the challenges and outlook are discussed.N

A phase-field model for the evaporation of thin film mixtures

The performance of solution-processed solar cells strongly depends on the geometrical structure and roughness of the photovoltaic layers formed during film drying. During the drying process, the interplay of crystallization and liquid-liquid demixing leads to structure formation on the nano- and microscale and to the final rough film. In order to better understand how the film structure can be improved by process engineering, we aim at theoretically investigating these systems by means of phase-field simulations. We introduce an evaporation model based on the Cahn-Hilliard equation for the evolution of the fluid concentrations coupled to the Allen-Cahn equation for the liquid-vapour phase transformation. We demonstrate its ability to match the experimentally measured drying kinetics and study the impact of the parameters of our model. Furthermore, the evaporation of solvent blends and solvent-vapour annealing are investigated. The dry film roughness emerges naturally from our set of equations, as illustrated through preliminary simulations of spinodal decomposition and film drying on structured substrates