Entropy-Driven Reversible Melting and Recrystallization of Layered Hybrid Perovskites

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Layered 2D A₂PbX₄ perovskites typically decompose at high temperatures.
• Designing perovskites for lower melting points without decomposition is crucial for advanced applications.

Purpose of the Study:

• Investigate the thermodynamic driving forces for melting in layered perovskites.
• Develop strategies to lower the melting temperature of A₂PbX₄ perovskites.
• Enable solvent- and vacuum-free fabrication of perovskite films.

Main Methods:

• Considered perovskite melts as ionic liquid mixtures.
• Hypothesized that increased structural entropy of fusion (ΔS_fus) lowers melting temperature.
• Designed A-site cations with rigid solid-state structures and flexible molten states.

Main Results:

• Synthesized six A₂PbX₄ crystals exhibiting high ΔS_fus and low melting temperatures.
• [I-(CH₂)₃-NH₂(CH₃)]₂PbI₄ reversibly melted at 388 K, below its decomposition temperature of 500 K.
• Demonstrated melt-pressed, solvent- and vacuum-free perovskite films.

Conclusions:

• Structural entropy of fusion is the key thermodynamic parameter governing the melting behavior of layered perovskites.
• Tailoring A-site cation design can effectively tune ΔS_fus and melting points.
• This approach offers a viable route for fabricating high-quality perovskite films for optoelectronics.