Alloying Strategy Enables Record-Low Melting Temperature in 2D Metal Halide Perovskites

Abstract

Reduction of melting temperature (Tm) 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 Tm, which has been systematically investigated through a case study involving the synthesis of 1x21-x and 1x31-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 Tm and enthalpy changes of the hybrid systems exhibit concentration-dependent variations as characteristics of non-solid solution binary mixtures. Notably, 10.6020.40 exhibits a record-low Tm 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 10.5530.45 system exhibiting the Tm of 80 °C. This mixing entropy-driven approach provides both a practical pathway for Tm reduction in 2D MHPs and insights into the design of non-solid solution binary mixtures systems.