All‐inorganic perovskite solar cells (PSCs) have developed rapidly in the field of photovoltaics due to their excellent thermal and light stability. However, compared with organic–inorganic hybrid perovskites, the phase instability of inorganic perovskite under humidity still remains as a critical issue that hampers the commercialization of inorganic PSCs. We originally propose in this work that microstrains between the perovskite lattices/grains play a key role in affecting the phase stability of inorganic perovskite. To this end, we innovatively design the π‐conjugated p‐type molecule bis(2‐ethylhexyl) 3,3′((4,8‐bis(5‐(2‐ethylhexyl)‐3,4‐difluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(3,3″‐dioctyl[2,2′:5′,2″‐terthiophene]‐5″,5‐diyl))(2E,2′E)‐bis(2‐cyanoacrylate) (BTEC‐2F) to covalent with the Pb dangling bonds in CsPbI2Br perovskite film, which significantly suppress the trap states and release the defect‐induced local stress between perovskite grains. The interplay between the microstrains and phase stability of the inorganic perovskite are scrutinized by a series of characterizations including x‐ray photoelectron spectroscopy, photoluminescence, x‐ray diffraction, scanning electron microscopy, and so forth, based on which, we conclude that weaker local stresses in the perovskite film engender superior phase stability by preventing the perovskite lattice distortion under humidity. By this rational design, PSCs based on CsPbI2Br perovskite system deliver an outstanding power conversion efficiency (PCE) up to 16.25%. The unencapsulated device also exhibits an exceptional moisture stability by retaining over 80% of the initial PCE after 500 h aging in ambient with relative humidity of (RH) 25%.
Formamidinium lead triiodide (FAPbI 3 ) has been demonstrated as the most efficient perovskite system to date, due to its excellent thermal stability and an ideal bandgap approaching the Shockley-Queisser limit. Whereas, there are intrinsic quantum confinement effects in FAPbI 3 , which lead to unwanted non-radiative recombination. Additionally, the black α-phase of FAPbI 3 is unstable under room temperature due to the significant residual tensile stress in the film. To simultaneously address the above issues, a thermallyactivated delayed fluorescence polymer P1 is designed in the study to modify the FAPbI 3 film. Owing to the spectral overlap between the photoluminescence of P1 and absorption of the above-bandgap quantum wells of FAPbI 3 , the Förster energy transfer occurs at the P1/FAPbI 3 interface, which further triggers the Dexter energy transfer within FAPbI 3 . The exciton "recycling" can thus be realized, which reduces the non-radiative recombination losses in perovskite solar cells (PSCs). Moreover, P1 is found to introduce compressive stress into FAPbI 3 , which relieves the tensile stress in perovskite. Consequently, the PSCs with P1 treatment achieve an outstanding power conversion efficiency (PCE) of 23.51%. Moreover, with the alleviation of stress in the perovskite film, flexible PSCs (f-PSCs) also deliver a high PCE of 21.40%.
Abstract:In this paper, a 2D numerical model that is more physically realistic was established to simulate the complete process of Ti/Al explosive welding. Basing on the ANSYS/AUTODYN software package, the smoothed particle hydrodynamics (SPH) and arbitrary Lagrangian-Eulerian (ALE) were used for running this simulation. The numerical model can capture the typical physics in the explosive welding process, including the expansion of explosives, flyer plate bending, the impact of metal plates, jetting, and the wavy interface. The variable physical parameters during the explosive welding process were discussed. Most parts of the jet originated from the aluminum plate. According to the model, the jet velocity reached 7402 m/s. The pressure at the detonation point was too small to make the two plates to bond. The pressure could reach an order of magnitude of 10 7 kPa when the detonation energy tended to be stable and was far more than the yield strength of both materials, which resulted in an obvious narrow region of plastic strain emerging close to the collision zone. The signs of shear stresses between the two plates were the opposite. The interface morphology changed from straight to wave along the propagation of the detonation wave in the simulation, which was consistent with the experimental results.
With rapid development of photovoltaic technology, flexible perovskite solar cells (f-PSCs) have attracted much attention for their light weight, high flexibility and portability. However, the power conversion efficiency (PCE) achieved so far is not yet comparable to that of rigid devices. This is mainly due to the great challenge of depositing homogeneous and high-quality perovskite films on flexible substrate. In this study, the pre-buried 3-aminopropionic acid hydroiodide (3AAH) additives into the electron transport layer (ETL) and modified the ETL/perovskite (PVK) interface by a bottom-up strategy. 3AAH treatment induced a templated perovskite grain growth and improved the quality of the ETL. By this, the residual stresses generated in PVK during the annealing-cooling process are released and converted into micro-compressive stresses. As a result, the defect density of f-PSCs with pre-buried 3AAH is reduced and the photovoltaic performance is greatly improved, reaching an exceptional PCE of 23.36%. This strategy provides a new idea to bridge the gap between flexible and rigid devices.
Friction stir welding (FSW) is well recognized as a very practical technology for joining magnesium alloys. Although, a large amount of progress have been made on the FSW of magnesium alloys, it should be emphasized that many challenges still remain in joining magnesium using FSW. In this article, we briefly review the background of friction stir welding of magnesium alloys, and then focus on the effects of the friction stir welding on the macrostructure, microstructure evolution, texture distribution, and the mechanical properties of the welding joints. The macro-defects in welds and their relationship to the welding parameters such as welding speed, rotation speed, and axial force were also discussed. The review concluded with some suggested methods improvement and future challenges related to FSW of magnesium alloys. The purpose of the present review paper is to fully understand the relationships between the microstructure and the properties, and then establish a global, state-of-the-art FSW of magnesium alloys.
The ternary strategy is an effective method to improve the efficiency of organic solar cells (OSCs). Herein, high‐performance OSCs with over 18% efficiency using PM6 as donor and alloy‐like acceptor containing two highly structurally similar acceptors (Y6 and Y6‐1O) is obtained. The spectral overlap of Y6 and Y6‐1O can increase the collection of photons via enhancing the absorption in near infrared region, which is conducive to improve the short‐circuit current density (J
SC). Meanwhile, beneficial electron transport channels are established by the construction of cascaded energy levels of Y6 and Y6‐1O in the ternary films. In addition, compared with Y6‐ and Y6‐1O‐based binary devices, enhanced charge mobility and suppressed charge recombination are observed in the optimal ternary OSCs, contributing to better performance. The improved performance of ternary devices based on the introduction of Y6‐1O is also attributed to the enhancement of photon capture and improved charge extraction as well as optimized blend morphology. A very promising ternary strategy is presented with two highly compatible acceptors to synergize the device performance in the development of high‐efficient OSCs.
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