High-efficiency hybrid halide perovskites: a complex material with a simple start in the crystallization process

Area of Science:

• Materials Science
• Solid State Chemistry
• Optoelectronics

Background:

• Halide perovskites (HPs) are crucial for optoelectronic devices, especially photovoltaics, with efficiencies reaching 27.3%.
• Understanding the early-stage crystallization of HPs from solution is vital for optimizing device performance.
• The role of the A-site cation in HP precursor solution chemistry remains incompletely understood.

Purpose of the Study:

• To investigate the influence of A-site cations on the atomic arrangement of iodoplumbate species in HP precursor solutions.
• To explore the impact of different solvents and A-site cations on HP crystallization pathways.
• To extend the core-shell model for describing HP precursor solutions with inorganic A-cations.

Main Methods:

• Small-angle X-ray scattering (SAXS) was used to analyze precursor solutions of various inorganic (NaPbI3, KPbI3, RbPbI3, CsPbI3) and mixed-cation (Cs0.05(FA0.98MA0.02)0.95Pb(I0.98Br0.02)3) halide perovskites.
• Solutions were prepared using γ-butyrolactone (GBL), dimethylformamide (DMF), and DMF:DMSO solvents.
• The extended core-shell model was applied to interpret SAXS data and understand atomic arrangements.

Main Results:

• Alkali-metal A-cations in HP solutions lead to shorter interparticle distances compared to organic A-cations (formamidinium/methylammonium).
• Fully inorganic HPs favor corner-sharing octahedra in the core, while mixed-cation HPs favor single-octahedron cores.
• Halide composition has a greater influence on atomic arrangement in solution than the A-site cation.

Conclusions:

• The A-site cation significantly modifies the atomic arrangement in HP precursor solutions.
• The halide composition plays a more critical role than the A-site cation in determining the atomic structure of species in solution.
• Precursor chemistry, influenced by cation and halide composition, impacts crystallisation pathways and ultimately device performance.