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Continuous discoveries in the field of metallic conductive MXenes have shown their feasibility as electrode materials, but their employment remains impeded by low surface area and inhomogeneous edge terminations generated by hazardous HF etching. To solve these problems, for the first time, a eutectic mixture etching strategy is utilized to accomplish one‐step synthesis of Cl‐terminated MXene (Ti3C2Cl2) with tunable in‐plane porosity from a MAX precursor (Ti3AlC2) through manipulating the phase transition of the selected salt melt. Specifically, the temperature and composition of the NaCl/ZnCl2 salt mixture are controlled to initiate a mechanism that creates and critically preserves the MXene pore structure, leading to substantial increment in material mesoporosity and a fourfold increase in surface area. Moreover, X‐ray spectroscopy analyses reveal increased TiC6 octahedral symmetry and density functional theory (DFT) modeling suggests a lower Li diffusion barrier, which imply high suitability for ion transport. Benefiting from these optimizations, mesoporous Ti3C2Cl2 delivers a high capacity of 382 mAh g−1 at 0.1 A g−1 as a dual‐ion battery anode, with capacity retention over 89% after 1000 cycles at 2.0 A g−1. Overall, this study presents a green chemistry approach that enables direct synthesis of MXenes with optimal porosity and surface termination for electrochemical applications, providing fresh insights for targeted structure modifications. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are considered to be a promising candidate for near‐space applications due to their high specific power, excellent radiation resistance, and compatibility with flexible substrates. Nevertheless, the low‐temperature cycles impose considerable challenges to their long‐term stability. Herein, the extremely low‐temperature photovoltaic process of PSCs is investigated and the effect mechanisms of PAN (Polyacrylonitrile) as an additive are revealed. It is found that the additive PAN regulates perovskite lattice stress and stabilizes perovskite lattice structure and thus retards perovskite phase transition at low temperatures. Moreover, the PAN improves perovskite dielectric properties and ion migration activation energy and effectively passivates perovskite defects at low temperatures. Therefore, the carrier transport/extraction/collection abilities at low temperatures are enhanced effectively by alleviating exciton effect and increasing dielectric screening effect. Benefiting from these positive effects of PAN, the PAN‐modified device achieves a maximum efficiency of 24.34% at 150K and maintains 72% of its initial value after 120 thermal cycles (290‐130K). Also, the PAN‐modified flexible devices exhibit excellent bending stability and thermal cycle stability. This study provides a deep insight into understanding the extremely low‐temperature photovoltaic behavior of PSCs and demonstrates the potentiality of PAN additive strategy for achieving efficient and stable PSCs at low temperatures. [ABSTRACT FROM AUTHOR]