Effect of different deposition sequences on the magnetic properties of sintered Nd–Fe–B magnets diffused with multicomponent Tb–Cu films

To further investigate the impact of layered deposition process on the magnetic properties of sintered Nd–Fe–B magnets, the multicomponent Tb–Cu films with different deposition sequences were designed through magnetron sputtering system. We first examined the effects of heat treatment, pure Cu and pure Tb diffusion on the magnetic properties of original magnets. For multicomponent Tb–Cu diffused magnets, we found that the deposition amount of Cu was an important factor in studying the diffusion mechanism of Tb–Cu films during grain boundary diffusion process. The deposition of Cu in moderation could significantly increase the diffusion depth of Tb due to the reduction in the enrichment of Tb near the surface. The deposition of excessive Cu reduced the diffusion efficiency of Tb, even lower than that of Tb in pure Tb diffused magnet. The results showed that the sequence of Tb deposition followed by Cu deposition in moderation was the optimal deposition order to achieve higher synthetical magnetic properties. Moreover, we investigated the negative impact of the Tb-rich zone on magnetic properties and proposed structural models for different diffused magnets

Research on shutdown purge characteristics of proton exchange membrane fuel cells: Purge parameters conspicuity and residual water

This paper comprehensively investigates the purge mechanism of proton exchange membrane fuel cells during the shutdown process, which qualitatively examines the effect of purge parameters (including current density, stoichiometric ratio, and relative humidity) on water content variation, and further quantitatively investigates the remaining water content post-purge. In contrast to previous studies, this paper offers a novel perspective on analyzing the purge process and conducts a thorough examination of residual water content. This study presents a transient, isothermal, two-phase flow model for proton exchange membrane fuel cells, which is subsequently validated experimentally. Results indicate that the significance of purge parameters follows the descending order: stoichiometric ratio, relative humidity, and current density. During the purge, the stoichiometric ratio should be rapidly increased to above 9. Each incremental rise in the stoichiometric ratio from 6 to 14 leads to a respective reduction in residual membrane water content after purge of 2.19 %, 1.57 %, 1.18 %, 0.93 %, 0.76 %, 0.63 %, 0.53 %, and 0.46 %. Similarly, it is recommended to swiftly decrease relative humidity to below 40 %. Elevating the purge current density from 20 to 200 mA/cm2 decreases the time required to completely remove liquid water from 20.24 s to 6.59 s. Hence, employing a higher current density at the onset of the purge facilitates quicker removal of liquid water, albeit resulting in an increase in residual membrane water content post-purge, from 3.17 to 3.70. In summary, optimizing the purge strategy requires adjusting purge current densities according to the specific purge stage.Design & Construction Managemen

Influence of Hole Transport Layers on Buried Interface in Wide-Bandgap Perovskite Phase Segregation

Light-induced phase segregation, particularly when incorporating bromine to widen the bandgap, presents significant challenges to the stability and commercialization of perovskite solar cells. This study explores the influence of hole transport layers, specifically poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), on the dynamics of phase segregation. Through detailed characterization of the buried interface, we demonstrate that Me-4PACz enhances perovskite photostability, surpassing the performance of PTAA. Nanoscale analyses using in situ Kelvin probe force microscopy and quantitative nanomechanical mapping techniques elucidate defect distribution at the buried interface during phase segregation, highlighting the critical role of substrate wettability in perovskite growth and interface integrity. The integration of these characterization techniques provides a thorough understanding of the impact of the buried bottom interface on perovskite growth and phase segregation

Passivating Defects of Perovskite Solar Cells with Functional Donor-Acceptor-Donor Type Hole Transporting Materials

In this study, a series of donor-acceptor-donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb-N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods

Junction Quality of SnO₂‑Based Perovskite Solar Cells Investigated by Nanometer-Scale Electrical Potential Profiling

Electron-selective layers (ESLs) and hole-selective layers (HSLs) are critical in high-efficiency organic–inorganic lead halide perovskite (PS) solar cells for charge-carrier transport, separation, and collection. We developed a procedure to assess the quality of the ESL/PS junction by measuring potential distribution on the cross section of SnO₂-based PS solar cells using Kelvin probe force microscopy. Using the potential profiling, we compared three types of cells made of different ESLs but otherwise having an identical device structure: (1) cells with PS deposited directly on bare fluorine-doped SnO₂ (FTO)-coated glass; (2) cells with an intrinsic SnO₂ thin layer on the top of FTO as an effective ESL; and (3) cells with the SnO₂ ESL and adding a self-assembled monolayer (SAM) of fullerene. The results reveal two major potential drops or electric fields at the ESL/PS and PS/HSL interfaces. The electric-field ratio between the ESL/PS and PS/HSL interfaces increased in devices as follows: FTO < SnO₂-ESL < SnO₂ + SAM; this sequence explains the improvements of the fill factor (FF) and open-circuit voltage (<i>V</i>_oc). The improvement of the FF from the FTO to SnO₂-ESL cells may result from the reduction in voltage loss at the PS/HSL back interface and the improvement of <i>V</i>_oc from the prevention of hole recombination at the ESL/PS front interface. The further improvements with adding an SAM is caused by the defect passivation at the ESL/PS interface, and hence, improvement of the junction quality. These nanoelectrical findings suggest possibilities for improving the device performance by further optimizing the SnO₂-based ESL material quality and the ESL/PS interface

Pure 2D Perovskite Formation by Interfacial Engineering Yields a High Open‐Circuit Voltage beyond 1.28 V for 1.77‐eV Wide‐Bandgap Perovskite Solar Cells

Abstract Surface post‐treatment using ammonium halides effectively reduces large open‐circuit voltage (VOC) losses in bromine‐rich wide‐bandgap (WBG) perovskite solar cells (PSCs). However, the underlying mechanism still remains unclear and the device efficiency lags largely behind. Here, a facile strategy of precisely tailoring the phase purity of 2D perovskites on top of 3D WBG perovskite and realizing high device efficiency is reported. The transient absorption spectra, cross‐sectional confocal photoluminescence mapping, and cross‐sectional Kelvin probe force microscopy are combined to demonstrate optimal defect passivation effect and surface electric‐field of pure n = 1 2D perovskites formed atop 3D WBG perovskites via low‐temperature annealing. As a result, the inverted champion device with 1.77‐eV perovskite absorber achieves a high VOC of 1.284 V and a power conversion efficiency (PCE) of 17.72%, delivering the smallest VOC deficit of 0.486 V among WBG PSCs with a bandgap higher than 1.75 eV. This enables one to achieve a four‐terminal all‐perovskite tandem solar cell with a PCE exceeding 25% by combining with a 1.25‐eV low‐bandgap PSC