Metal halide perovskites (MHPs) have garnered significant attention due to their distinctive optical and electronic properties, coupled with excellent processability. However, the thermal characteristics of these materials are often overlooked, which can be harnessed to cater to diverse application scenarios. We showcase the efficacy of lowering the congruent melting temperature (T_m) of layered 2D MHPs by employing a strategy that involves the modification of flexible alkylammonium through N-methylation and I-substitution. Structural–property analysis reveals that the N-methylation and I-substitution play pivotal roles in reducing hydrogen bond interactions between the organic components and inorganic parts, lowering the rotational symmetry number of the cation and restricting the residual motion of the cations. Additional I···I interactions enhance intermolecular interactions and lead to improved molten stability, as evidenced by a higher viscosity. The 2D MHPs discussed in this study exhibit low T_m and wide melt-processable windows, e.g., (DMIPA)₂PbI₄ showcasing a low T_m of 98 °C and large melt-processable window of 145 °C. The efficacy of the strategy was further validated when applied to bromine-substituted 2D MHPs. Lowering the T_m and enhancing the molten stability of the MHPs hold great promise for various applications, including glass formation, preparation of high-quality films for photodetection, and fabrication of flexible devices.

中文翻译：

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低同熔温度和大熔融加工窗口二维金属卤化物钙钛矿的合理设计

金属卤化物钙钛矿（MHP）因其独特的光学和电子性能以及优异的加工性能而受到广泛关注。然而，这些材料的热特性常常被忽视，但可以利用这些特性来满足不同的应用场景。我们展示了通过采用涉及通过N-甲基化和 I-取代对柔性烷基铵进行修饰的策略来降低层状 2D MHP 的全等熔化温度 ( T _m )的功效。结构性质分析表明，N-甲基化和I-取代在减少有机组分和无机部分之间的氢键相互作用、降低阳离子的旋转对称数和限制阳离子的残余运动方面发挥着关键作用。额外的 I·I 相互作用增强了分子间相互作用，并导致熔融稳定性提高，这一点可以通过更高的粘度来证明。本研究中讨论的2D MHP 表现出低T _m和宽的熔融加工窗口，例如，(DMIPA) ₂ PbI ₄表现出98 °C 的低T _m和145 °C 的大熔融加工窗口。当应用于溴取代的二维 MHP 时，该策略的有效性得到了进一步验证。降低MHP 的T _m并增强其熔融稳定性为各种应用带来了巨大的前景，包括玻璃形成、用于光电检测的高质量薄膜的制备以及柔性器件的制造。