Thermal and Optical Properties of Meltable Two-Dimensional Hybrid Perovskite Blends

Melt processing is a common practice for handling materials. In classic metallurgy, for example, it is widely used for alloying: the pure metals are heated above their melting point, followed by mixing and subsequently cooling. This process often yields alloys with distinct thermal, electrical, and optical properties compared to their constituent metals, primarily dictated by the chemical composition, i.e., the identity and relative amount of each metal.<br/>Recently, it was shown that two-dimensional hybrid organic-inorganic perovskites (2D-HOIPs), with the chemical formula of (RNH₃)₂MX₄ (where R is an organic moiety, M is a divalent metal cation, and X is a halide) can undergo melting upon heating. These materials demonstrate a tremendous potential to be implemented in next-generation optoelectronic applications. Leveraging this meltability offers a promising solvent-free fabrication approach with potential enhancements in performance metrics.<br/>In this research, we explore the alloying behaviours of 2D-HOIPs, specifically analysing (1-MHA)₂PbI₄ (where 1-MHA = 1-methylhexylamine) and (S-NEA)₂PbBr₄ (where S-NEA = (S)-(−)-1-(1-naphthyl)ethylamine), which are examples of liquid-forming and glass-forming 2D-HOIPs, respectively. Thermal analysis of the blends has revealed significant changes in both melting and glass transition temperatures, compared to the pure 2D-HOIPs. Furthermore, optical absorbance measurements have shown variations in the band gap of these blends during melting, and again after the recrystallization of the glassy perovskite.