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Magnetic reconnection is a fundamental physical process of rapidly converting magnetic energy into particles. The electron diffusion region (EDR) is the crucial region during magnetic reconnection. The outer EDR, which also plays a crucial role in magnetic reconnection, is responsible for energy conversion. In the outer EDR, the electrons are decelerated and return the energy to the magnetic field on the pileup region behind the reconnection front. In the present study, we used the fully kinetic particle‐in‐cell simulation and revealed that part of decelerated electrons in the outer EDR could even move back to the inner EDR. This phenomenon is caused by the dominant contribution from the magnetic tension force, and it suggests a magnetic Marangoni effect in space plasma, similar to the Marangoni effect in fluids. Our results potentially propose a brand‐new physical process and a novel mechanism in the EDR during magnetic reconnection. Plain Language Summary Plasma's energy can be changed through various approaches in the universe, and magnetic reconnection is one of those approaches to convert energy from the magnetic field to the plasma. In the reconnection site, the inner electron diffusion region (EDR) is an essential area where the energy is released, and the electron's energy is enhanced significantly. Meanwhile, in the outer EDR, the electrons are decelerated by the electric field, thus their energy decreases. However, part of those electrons can move backward to the inner EDR, and how this phenomenon comes up has no further investigation. In this study, we use numerical simulations to reveal the possible mechanism of this kind of electron's motion. It is found that the electron deceleration is caused by the magnetic tensor force. The electrons with specific conditions have the possibility to move backward. Those backflow electrons have a second chance to be accelerated again in the inner EDR. Such electron motion in plasma physics is not a kind of gyro movement but might indicate a so‐called magnetic Marangoni effect similar to the Marangoni effect in fluid physics. Our findings propose a novel mechanism associated with electron acceleration in the EDR during magnetic reconnection. Key Points The magnetic tension force causes the deceleration of the electrons in the outer electron diffusion region (EDR) during magnetic reconnection Partial electrons are decelerated and even move back to the inner EDR, and they are accelerated again and attain higher energy The electron backflow motion in the outer EDR indicates a magnetic Marangoni effect in space plasma

In the prevailing form of the generalized Ohm's law (GOL), −me/e(J/en)⋅∇(J/en)${-}\\left({m}_{e}/e\\right)\\left[(\\boldsymbol{J}/en)\\cdot \\nabla \\right](\\boldsymbol{J}/en)$is often neglected. Because of the resemblance to the magnetic tension, we refer to this term as the current tension electric field (ECT). Our theoretical analysis reveals that ECT with a characteristic length of mi/me1/6λe${\\left({m}_{i}/{m}_{e}\\right)}^{1/6}{\\lambda }_{e}$dominates the electron inertia terms in the electron diffusion region (EDR) and is comparable to the electron pressure term in low‐βe conditions. Using particle‐in‐cell simulations, we demonstrate that ECT can contribute significantly to the reconnection electric field and energy dissipation at the boundaries of the inner EDR and in the outer EDR. Positive and negative J ⋅ ECT can be used to identify inner and outer electron diffusion regions, respectively. Plain Language Summary Magnetic reconnection is a fundamental physical process which allows for the explosive release of magnetic energy into thermal and kinetic energy. It underlies many dynamic phenomena in the universe, including solar eruptions, geomagnetic substorms and tokamak disruptions. In collisionless plasma, the generalized Ohm’s law (GOL) introduces collisionless effects which break the frozen‐in constraint and enable reconnection to occur. The term, −me/e(J/en)⋅∇(J/en)${-}\\left({m}_{e}/e\\right)\\left[(\\boldsymbol{J}/en)\\cdot \\nabla \\right](\\boldsymbol{J}/en)$ , which is one of the electron inertia terms of GOL, is referred to as the current tension electric field (ECT) by us due to its mathematical resemblance to magnetic tension. In many classic textbooks and review papers, ECT is considered as a small quantity and thus is ignored. In this study, we present solid evidence from both theoretical studies and particle‐in‐cell (PIC) simulations to demonstrate that ECT dominates the electron inertia terms and plays important roles in providing reconnection electric field and energy dissipation in reconnection. Therefore, it should not be ignored. Based on our results, many classic textbooks in which ECT has been ignored must be modified. Key Points ECT dominates the electron inertia terms in the electron diffusion region (EDR) and thus cannot be ignored in the generalized Ohm's law ECT contribute significantly to the reconnection electric field and energy dissipation in the inner and outer EDRs Positive and negative J · ECT can be used to identify inner and outer EDRs, respectively

We report in situ observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheath by the Magnetospheric Multiscale mission. The MFR was rooted in the magnetopause and could be generated by magnetopause reconnection therein. A thin current sheet was generated due to the interaction between MFR and MH. The sub‐Alfvénic ion bulk flow and the Hall field were detected inside this thin current sheet, indicating an ongoing reconnection. An elongated electron diffusion region characterized by non‐frozen‐in electrons, magnetic‐to‐particle energy conversion, and crescent‐shaped electron distribution was detected in the reconnection exhaust. The observation provides a mechanism for the dissipation of MFRs and thus opens a new perspective on the evolution of MFRs at the magnetopause. Our work also reveals one potential fate of the MHs in the magnetosheath which could reconnect with the MFRs and further merge into the magnetopause. Plain Language Summary Magnetic flux rope (MFR) is a kind of helical magnetic field structure that is frequently observed in the Earth's magnetosphere. At the dayside magnetopause, MFRs are generally generated by the reconnection of the Earth's intrinsic magnetic field and the interplanetary magnetic field, especially when the interplanetary magnetic field points southward. These MFRs tend to grow larger after they are expelled from the reconnection sites and then travel along the magnetopause, and ultimately disintegrate into the cusp. In this study, we provide another potential fate of these magnetopause MFRs. They can interact with the magnetosheath magnetic holes and dissipate through reconnection with multiple magnetic holes. Based on the Magnetospheric Multiscale observation, we provide direct evidence of reconnection between the MFR and the magnetic hole, which has a pivotal role in this scenario. Our results give new insights into the evolution of MFRs at the magnetopause and further the coupling between the solar wind and the Earth's magnetosphere. Key Points First observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheath A thin current sheet with typical reconnection signatures was formed at the interface of MFR and MH due to their interaction An elongated electron diffusion region was detected in the reconnection exhaust

Using high‐resolution data from Magnetospheric Multiscale (MMS) mission, we report an intense current layer at the center of a flux rope (FR) in the magnetotail. The intense current layer is caused by the compression of the ion bulk flows at the center of a FR rather than two interlaced flux tubes reported at the magnetopause previously. The intense current layer has been identified as an electron diffusion region of the magnetic reconnection, and the hall magnetic field generated by magnetic reconnection makes the FR show crater‐shaped. The reconnecting current layer is supported by the poloidal magnetic field of the FR, and it is dividing the FR into two secondary FRs. The observations suggest that magnetic FR can be compressed easily to excite instability inside it as it is propagating in the magnetotail current sheet, thus changing its magnetic topology. Plain Language Summary Magnetic flux ropes (FRs) consist of a poloidal magnetic field and an axial magnetic field component and are always described as helical magnetic field structures. The FRs play an important role in particle acceleration, magnetic flux transportation, and the evolution of reconnection. Recently, with high‐resolution magnetic field and plasma moments measurements, it is found that the interior of the FR is active, and a lot of processes could occur therein. In this work, we report a FR embedded in an unstable tailward plasma flow in the magnetotail. An ongoing reconnection current layer is observed at the center of the FR. The reconnecting current layer could change the magnetic field topology of the initial FR and divide the initial FR into two secondary FRs. Key Points An electron diffusion region of reconnection is observed at the center of the flux rope (FR) in the magnetotail The reconnecting current layer can change the magnetic field topology inside the FR and divide it into two secondary FRs The Hall magnetic field inside the reconnecting current layer leads to the crater‐shaped magnetic field magnitude within the FR

In this letter, a non-equipotential surface photovoltaic effect is reported in nano metal-semiconductor structures. When the surface of the Ti/Si is uniformly illuminated by a beam of light, a controllable surface photovoltaic effect is observed on the metal side. The center of the surface presents a remarkably higher metallic potential than the surrounding region. The surface photovoltage is detected to be as high as 53 mV. Besides, it depends sensitively on the thickness and size of the metal films, demonstrating it is a unique feature of nano metal films. We ascribe this phenomenon to the boundary effect of photon-generated carriers in the ultrathin metal thickness. The theoretical calculations based on equivalent electron diffusion model are in great agreement with the experimental results. The results may promise some novel applications based on the nanoscale metal-semiconductor systems.

Ternary metal vanadates have recently emerged as promising photoelectrode materials for sunlight-driven water splitting. Here, we show that highly active nanostructured BiVO4 films can be deposited onto fluorine-doped tin oxide (FTO) substrates by a facile sequential dipping method known as successive ionic layer adsorption and reaction (SILAR). After annealing and deposition of a cobalt phosphate (Co-Pi) co-catalyst, the photoelectrodes produce anodic photocurrents (under 100 mW cm-2 broadband illumination, 1.23 V vs. RHE) in pH 7 phosphate buffer that are on par with the highest reported in the literature for similar materials. To gain insight into the reason for the good performance of the deposited films, and to identify factors limiting their performance, incident photon-to-electron conversion efficiency spectra have been analyzed using a simple diffusion–reaction model to quantify the electron diffusion length (Ln; the average distance travelled before recombination) and charge separation efficiency (ηsep) in the films. The results indicate that ηsep approaches unity at sufficiently positive applied potential but the photocurrent is limited by significant charge collection losses due to a short Ln relative to the film thickness. The Co-Pi catalyst is found to improve ηsep at low potentials as well as increase Ln at all potentials studied. These findings help to clarify the role of the Co-Pi co-catalyst and show that there could be room for improvement of BiVO4 photoanodes deposited by SILAR if Ln can be increased.

Dye-sensitized solar cells (DSSC) made of TiO2 have received considerable attention from many researchers for the last three decades. Rapid theoretical and experimental studies have been conducted to improve the performance of DSSC. To understand the DSSC internal parameters, we need to fine-tune each component and identify the suitable conditions in optimizing the performance of assembled devices. In this work, we analyzed and calculated of several parameters the DSSC photoanode, e.g. electron diffusion and photon absorption coefficients. The experimental I-V data from solar simulator measurements were fitted base on electron diffusion model using Microcal Origin software. We compared the photon absorption coefficient values from this calculation method with the result of UV-Vis measurement and compared the electron diffusion coefficient values with the result of the SEM image data fitting calculation method. It was apparent that the results of I-V data fitting calculation method were comparable with the results of two other techniques.

Developing multijunction perovskite solar cells (PSCs) is an attractive route to boost PSC efficiencies to above the single-junction Shockley-Queisser limit. However, commonly used tin-based narrow-bandgap perovskites have shorter carrier diffusion lengths and lower absorption coefficient than lead-based perovskites, limiting the efficiency of perovskite-perovskite tandem solar cells. In this work, we discover that the charge collection efficiency in tin-based PSCs is limited by a short diffusion length of electrons. Adding 0.03 molar percent of cadmium ions into tin-perovskite precursors reduce the background free hole concentration and electron trap density, yielding a long electron diffusion length of 2.72 ± 0.15 µm. It increases the optimized thickness of narrow-bandgap perovskite films to 1000 nm, yielding exceptional stabilized efficiencies of 20.2 and 22.7% for single junction narrow-bandgap PSCs and monolithic perovskite-perovskite tandem cells, respectively. This work provides a promising method to enhance the optoelectronic properties of narrow-bandgap perovskites and unleash the potential of perovskite-perovskite tandem solar cells. Tin-based perovskites possess the suitable narrow-bandgap for tandem solar cells but their short carrier diffusion lengths limit device efficiency. Here Yang et al . add cadmium ions to increase diffusion length to above 2 µm by reducing the background free hole concentration and electron trap density.

DSSC is a natural dye-based organic solar cell composed of layers of semiconductor (photoanode), dye, electrolyte, and the counter electrode. The photoanode layer on DSSC acts as a dye binder and can pass on excited electrons to the electrode counter. This component is one of the keys to improve the DSSC performance. The TiO2 material has been used widely as a photoanode due to its high stability to light so that at its optimum thickness it can pass well the sunlight energy on the surface of the DSSC. When the sunlight energy impinges to DSSC for relatively long time, it can increase the working temperature. Theoretically, the increase in the working temperature of the DSSC causes an increase in the electron diffusion coefficient in the DSSC, thus affecting its performance. Therefore, the interpretation of an increase in the electron diffusion coefficient due to an increase in the thickness and working temperature in DSSC is essential to be studied. In this article, a simulation of the determination of the optimum thickness of TiO2 photoanode was carried out. We studied the effect of electron diffusion coefficient on the DSSC open voltage at the optimum thickness. The highest electron diffusion coefficient in this simulation was 9.65x10-3 cm2/s with current density of 0.0145 A/cm2, voltage of 0.3411 V, power of 0.0020 V·A/cm2, and efficiency of 2.000%. We found that the higher the electron diffusion coefficient, the open voltage of DSSC increased so that its performance also increased.

Tandem solar cells involving metal-halide perovskite subcells offer routes to power conversion efficiencies (PCEs) that exceed the single-junction limit; however, reported PCE values for tandems have so far lain below their potential due to inefficient photon harvesting. Here we increase the optical path length in perovskite films by preserving smooth morphology while increasing thickness using a method we term boosted solvent extraction. Carrier collection in these films – as made – is limited by an insufficient electron diffusion length; however, we further find that adding a Lewis base reduces the trap density and enhances the electron-diffusion length to 2.3 µm, enabling a 19% PCE for 1.63 eV semi-transparent perovskite cells having an average near-infrared transmittance of 85%. The perovskite top cell combined with solution-processed colloidal quantum dot:organic hybrid bottom cell leads to a PCE of 24%; while coupling the perovskite cell with a silicon bottom cell yields a PCE of 28.2%. Metal-halide perovskite based tandem solar cells are appealing but making a high efficiency device is not trivial. Here Chen et al. increase the carrier collection in the perovskite layer and largely enhance the efficiency in tandem cells when combined with colloidal quantum dot or silicon layers.