Alloying strategy enables record-low melting temperature in 2D metal halide perovskites

Abstract

Reduction of melting temperature (T_m) stands as a pivotal challenge in advancing the applications of two-dimensional metal halide perovskites (2D MHPs). Herein, we employ an alloying strategy to effectively depress the T_m, which has been systematically investigated through a case study involving the synthesis of 1_x2_1−x and 1_x3_1−x mixed hybrid metal halide systems (1 = (MIPA)₂PbI₄, 2 = (MIPTA)₂PbI₄, 3 = (GABA)₂PbI₄, MIPA = N-methyliodopropylammonium, MIPTA = N-methyliodopentylammonium, and GABA = 4-ammoniumbutyric acid cation; x = 0–1). The T_m and enthalpy changes of the hybrid systems exhibit concentration-dependent variation as characteristics of partial solid solution binary mixtures. Notably, 1_0.602_0.40 exhibits a record-low T_m of 60 °C among 2D MHPs. The underlying mechanism of eutectic formation is elucidated through the critical role of mixing entropy in reducing the Gibbs free energy change during melting. The melt-processing capability and glass-forming ability of the mixed compounds are verified. The applicability of this strategy is further validated by the 1_0.553_0.45 system exhibiting a T_m of 80 °C. This mixing-entropy-driven approach provides both a practical pathway for T_m reduction in 2D MHPs and insights into the design of partial solid-solution binary mixture systems.