Melt Alloying of Two-Dimensional Hybrid Perovskites: Composition-Dependence of Thermal and Optical Properties.

Melt alloying, the process of melting a physical powder blend to create a homogeneous alloy, is widely used in materials processing. By carefully selecting the materials and their proportions, the physical properties of the resulting alloy can be precisely controlled. In this study, we investigate the possibility of utilizing melt alloying principles for meltable two-dimensional hybrid organic-inorganic perovskites (2D-HOIPs). We blend and melt mixtures of two selected 2D-HOIPs: the glass-forming (S-NEA)2PbBr4 (S-NEA = (S)-(-)-1-(1-naphthyl)ethylammonium) and the liquid-forming (1-MHA)2PbI4 (1-MHA = 1-methylhexylammonium). Upon melting and cooling, 1-MHA-poor blends (X1-MHA ≤ 50% mol, where X1-MHA corresponds to the relative molar concentration of (1-MHA)2PbI4 in the blend) form a hybrid glass, while 1-MHA-rich blends (X1-MHA ≥ 70% mol) crystallize. The melting temperature of all blends, as well as the glass transition temperature of the glass-forming blends, change according to blend composition. In all cases, melting produces a homogeneous structure, either glassy or crystalline, which remains such after the glassy samples are recrystallized upon a second heat treatment. This method enables band gap tuning of the blends, given that it varies with composition and crystallinity. Overall, this work demonstrates the applicability of classical melt processing to binary-component functional hybrid systems, and paves the way to solvent-free perovskite-based device fabrication.