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Metal halide perovskite with high Young's modulus is prone to form cracks when subjected to mechanical stresses such as bending, twisting, or impacting, ultimately leading to a permanent decline in the performance of their photovoltaic devices. These mechanical properties pose challenges to the durability of long‐term service of photovoltaic devices and the production of flexible devices. To address this issue, the poly (lipoic acid‐co‐Styrene) elastomer is employed to modulate the modulus of perovskite films. The peak force quantitative nanomechanical atomic force microscopy measurements and nanoindentation tests demonstrated a reduction in modulus, with the lower modulus preventing the formation of cracks and defects during deformation. Moreover, this approach also suppressed the non‐radiative recombination of perovskite solar cells by leveraging the interaction between functional groups and defects. Through this method, the rigid inverted devices attained a power conversion efficiency of 24.42% alongside remarkable stability. Concurrently, flexible inverted devices achieved a power conversion efficiency of 22.21%. This strategy offers a promising avenue for fabricating flexible perovskite solar cells and enhancing their mechanical durability. [ABSTRACT FROM AUTHOR]

Harmful Sn(IV) vacancies and uncontrolled fast crystallization commonly occur in tin–lead alloyed perovskite films. The typical dimethyl sulfoxide (DMSO) processing solvent is suggested to be the primary source of problems. Here, a DMSO‐free solvent strategy is demonstrated to obtain high‐performance Cs0.25FA0.75Pb0.5Sn0.5I3 solar cells. A rational solvent selection process via Hansen solubility parameters and Gutmann's donor number shows that N,N′‐dimethylpropyleneurea (DMPU) has a strong coordinate ability to form complete complexation with organic (formamidinium iodide) and inorganic (CsI, PbI2, and SnI2) components. This treatment suppresses the iodoplumbate (PbIn2‐n) or iodostannate (SnIn2‐n) preformed in precursor solution, thereby promoting pure intermediate complexes and retarding crystallization, realizing enlarged grain size, and improved film crystallinity. Additionally, it is demonstrated that DMPU‐based solvent system can further inhibit the oxidation of Sn(II) and reduced Sn(IV) content by nearly 75% due to its superior thermal and chemical stability. This DMSO‐free strategy generates a record efficiency of 22.41%, with a Voc of 0.88 V and a FF of 82.72% for the MA‐free Sn–Pb alloyed device. The unencapsulated devices display much‐improved humidity stability at 30 ± 5% relative humidity in air for 240 h, impressive thermal stability at 85 °C for 500 h, and promote continuous operation stability at maximum power point for 150 h. [ABSTRACT FROM AUTHOR]

Perovskite solar cells with increasingly pure composition of α‐formamidinium lead triiodide (α‐FAPbI3) perovskite are utilized to set more and more record‐breaking efficiencies. However, pure α‐FAPbI3 perovskite is unstable and difficult to prepare. Here, a series of bulky alkylammoniums known as the spacer cations (RP cations) of 2D Ruddlesden–Popper perovskites (2D perovskites) are used to prepare α‐FAPbI3 perovskite films. The deprotonation process of RP cations during annealing removes the in situ generated 2D perovskites from the film, which determines the phase and compositional purity, crystallinity, and stability of α‐FAPbI3 perovskite films and depends on the design of RP cations. Only a small number of residual RP cations (0.3–2.3%) are found anchoring at grain boundaries. As a result, α‐FAPbI3 perovskite solar cells prepared from RP cations, especially 2‐thiophenemethylammonium, show higher efficiency and stability than control devices prepared from the most commonly used methylammonium. It is believed that in situ generated 2D perovskites are ideal additives for α‐FAPbI3 perovskite, because a large addition (20%) of 2D perovskites ensures the preparation of high‐quality phase‐pure α‐FAPbI3 perovskite films, while a small number of residual RP cations anchored at grain boundaries guarantee the performance and stability of α‐FAPbI3 perovskite solar cells. [ABSTRACT FROM AUTHOR]

Transition of δ‐phase formamidinium lead triiodide (δ‐FAPbI3) to pure α‐phase FAPbI3 (α‐FAPbI3) typically requires high processing temperature (150 °C), which often results in unavoidable residual stress. Besides, using methylammonium chloride (MACl) as additive in fabrication will cause MA residue in the film, compromising the compositional purity. Here, a stress‐released and compositional‐pure α‐FAPbI3 thin‐film is fabricated using 3‐chloropropylammonium chloride (Cl‐PACl) by two‐step annealing. The 2D template of n = 2 can preferentially form in perovskite with the introduction of Cl‐PACl at a temperature as low as 80 °C. Such a 2D template can guide the free components to form ordered α‐FAPbI3 and promote the transition of the formed δ‐FAPbI3 to α‐FAPbI3 by reducing the phase transition energy. As a result, the obtained perovskite films via low‐temperature phase‐transition have a high degree of crystal orientation and reduced residual stress. More importantly, most of the Cl‐PACl is volatilized during the subsequent high‐temperature annealing process accompanied by the disintegration of the 2D templates. The residual trace of Cl‐PA+ is mainly concentrated at the grain boundary near the perovskite surface layer, stabilizing α‐FAPbI3 and passivating defects. Perovskite solar cell based on pure α‐FAPbI3 achieves a power conversion efficiency of 23.03% with excellent phase stability and photo‐stability. [ABSTRACT FROM AUTHOR]

Mixed‐halide perovskite has an irreplaceable role as wide‐bandgap absorber in multi‐junction tandem solar cells. However, large open‐circuit voltage (Voc) loss due to non‐uniform halide distribution and compromised device stability due to photo‐induced halide segregation has significantly limited the applications. Here, it is introduced 4‐(2‐aminoethyl)‐benzenesulfonyl fluoride hydrochloride (ABF) with multifunctional groups (sulfonyl, ammonium, and fluoride) to the mixed‐halide precursor to demonstrate a downward homogenized crystallization strategy for suppressing the initial vertical halide phase separation during perovskite crystallization and reducing Voc loss. Furthermore, fluoride with strong electronegativity effectively fixes anions and cations, while sulfonyl and ammonium are used to passivate positive charged (halide vacancies) and negative charged (FA/MA vacancies) defects, respectively, thereby reducing the generation of ion vacancies that lead to subsequent photo‐induced halide segregation. As a result, the 1.63 and 1.68 eV wide‐bandgap perovskite solar cells with inverted structures exhibit the champion power conversion efficiency (PCE) of 21.76% and 20.11% with Voc of 1.18 and 1.21 V, respectively. Most importantly, the optimized devices without encapsulation preserve 86% of initial efficiency after 240 h of continuous illumination under AM 1.5G, showing excellent light stability. Thus, the homogenized crystallization strategy provides highly efficient performance and stability for future tandem solar cell applications. [ABSTRACT FROM AUTHOR]

In sequential‐deposited polycrystalline perovskite solar cells, the unreacted lead iodide due to incomplete conversion of lead iodide to perovskite phase, can contribute to ionic defects, such as residual lead ions (Pb2+). At present, passivation of interfacial and grain boundary defects has become an effective strategy to suppress charge recombination. Here, we introduced potassium acetate (KAc) and potassium dichloroacetate (KAcCl2) as additives in the sequential deposition of polycrystalline perovskite thin films and found that acetate ions (Ac−) can effectively reduce the residual lead iodide. Compared with acetate (Ac), dichloroacetate (AcCl2) can form Pb−Cl and Pb−O bonding as "dual anchoring" bonds with residual Pb2+, resulting in strong binding force and effective passivation of residual Pb2+ defects. Furthermore, K+ can enlarge grain size and restrain ion migration at the grain boundaries. Consequently, perovskite solar cells with KAcCl2 additive show power conversion efficiencies (PCE) from 19.67 % to 22.12 %, with the open‐circuit voltage increasing from 1.06 V to 1.14 V. The unencapsulated device can maintain 82 % of the initial PCE under a humidity of 30±5 % for 1200 h. This work provides a new approach for the regulation of ionic defects and grain boundaries at the same time to develop high‐performance planar perovskite solar cells. [ABSTRACT FROM AUTHOR]

Formamidinium cesium (FACs) perovskite solar cells (PSCs) with the exclusion of methylammonium (MA) cations often have greatly improved device stability; however, their inferior performance compared with MA‐based devices has impeded the real application. Among various device engineering strategies, bottom interfacial engineering is a promising method to simultaneously achieve the passivation of interfacial defects and the crystallization control of perovskite. Herein, a simple and effective bottom interfacial design is presented to improve the efficiency and stability of FACs PSCs by capping o‐phenanthroline derivatives on the ZnO electron transporting layer (ETL). The most efficient modifier, 4,7‐Dichloro‐1,10‐phenanthroline (Cl‐phen), can improve the crystallinity of the perovskite film by chlorinated surface and passivate the defects of ZnO by reducing surface hydroxyl groups and oxygen vacancies. In addition, Cl‐phen modified ZnO shows better energy alignment with FACs perovskite and increases the built‐in electric field cascade by 80 mV. As a result, a champion device efficiency of 21.15% is obtained using ZnO/Cl‐phen bilayer ETL. The stability has also been improved using ZnO/Cl‐phen bilayer ETL, in which 91.5% of initial PCE is retained after 1500 h of storage at ambient environment (RH: 40–50%) without encapsulation. [ABSTRACT FROM AUTHOR]

During the service life of metro vehicles, the cracks frequently appear at the root of motor seats. This indicates the previous antifatigue designs are unable to cover the actual operating environment. Some individual loads, such as motor vibration, have been ignored or wrongly understood, which leads to the occurrence of local insufficient fatigue life of the frame. To illustrate the influence of the motor vibration on the fatigue life of the bogie frame, a metro vehicle was taken as an example: first, the precise finite element model of the frame was established, and its correctness was verified; then, the vibration characteristics of the frame were analyzed by sweep frequency calculation; and finally, considering the vibration acceleration signal of the motor measured on a metro line as the excitation, the influence of the random vibration on the fatigue life of the frame under traction and idle running conditions was compared and analyzed by solving the power spectral density of the dynamic stress response at the weak fatigue nodes of the structure. The results show that the energy of the vibration in the frame is mainly concentrated in modes 6 and 7, which are excited by the motor transverse and vertical vibration, respectively, and contribute a lot to the fatigue damage of the frame; the fatigue life of the vital positions of the frame under the traction condition significantly reduces compared to the idle running condition; and the contribution of the low-amplitude vibration above 300 Hz to the fatigue damage can be ignored. At last, the importance of the influence of the motor traction vibration on the fatigue life should be fully considered in the metro vehicle design was proposed. [ABSTRACT FROM AUTHOR]

High εHf(t) intermediate‐felsic rocks have been found in some world‐famous orogenic belts and are considered as one useful proxy for modelling crustal growth. In contrast, low εHf(t) felsic rocks are generally derived from reworked ancient crust. In this study, we identified some Permian high zircon εHf(t) andesite, rhyolite, granodiorite and quartz diorite along the Solonker suture zone. The andesite (270 ± 3 Ma) shows high‐zircon εHf(t) (+4.7 to +7.9) and high‐Mg (Mg# = 42–75) values, high Sr contents (263–401 ppm) and Sr/Y ratios (13–24), akin to typical high‐Mg andesite, and are derived from a metasomatised source modified by the slab‐derived fluid/melt. The rhyolites (282 ± 2 Ma and 279 ± 2 Ma) show positive εHf(t) values (+3.4 to +14.9) and I‐type granite affinity. The granodiorite (295 ± 3 Ma) and quartz diorite (285 ± 1 Ma) are also characterised by high εHf(t) values, high‐K calc‐alkaline and I‐type granitoid compositions, but high A/CNK values (1.08–1.47) and CIPW‐normative corundum (1.61–5.56 vol%), due to late‐alteration induced low Na2O + K2O contents. The I‐type rhyolite and granitoid may have been formed by dehydration melting of sub‐alkaline meta‐basalts (mafic lower crust). The high‐Mg andesite, I‐type rhyolite and granitoids in this study were generated in a continental arc setting related to the Permian divergent double subduction of the Paleo‐Asian Ocean. The high εHf(t) Elitu andesites represent the lateral juvenile continental crust, and high εHf(t) felsic rocks represent mafic‐lower continental crust reworking. [ABSTRACT FROM AUTHOR]