Role of the Alkali Metal Cation in the Early Stages of Crystallization of Halide Perovskites

Abstract

ABX3 metal halide perovskites revolutionized the research and development of new optoelectronics, including solar cells and light-emitting diodes. Processing polycrystalline thin films from precursor solutions is one of the core advantages of these materials since it enables versatile and cost-effective manufacturing. The perovskite film morphology, that is, continuous substrate coverage and low surface roughness, is of paramount importance for highly efficient solar cells and optoelectronic devices in general. Controlling the chemistry of precursor solutions is one of the most effective strategies to manage the perovskite film morphology. Herein, we show the fundamental influence of the A-site cation composition on the perovskite precursor arrangement and the consequent film formation. Extended X-ray absorption fine structure spectroscopy and small-angle X-ray scattering give unprecedented insights into the complex structural chemistry of the perovskite precursors and, in particular, their repulsive interactions as a crucial parameter for colloidal stability. Combining these techniques with in situ grazing incidence wide-angle X-ray scattering during thin-film formation allows us to identify the mechanism for using alkali metals as a decisive criterion to control the colloidal stability of the perovskite precursor and thus the thin-film morphology. We illustrate the fundamental principle behind the systematic use of alkali metals regardless of whether they are incorporated in the lattice or not. Hence, this work provides tools to selectively control the morphology and crystal growth in present and future systems.

Recent progress of crystal orientation engineering in halide perovskite photovoltaics

“…19 Besides, it was reported that the organic ions in a conventional DMF or DMF/DMSO based perovskite precursor solution are not restricted inside the PbI 3 − inorganic framework, resulting in the emergence of an electrical double layer made of the respective counter ions surrounding the iodoplumbates and a diffuse layer. 126 Nevertheless, the single-crystal based perovskite precursor solution has been demonstrated to inherit the exceptional characteristics of the parent perovskite crystals, and fabricate the high-quality perovskite films with enhanced crystallinity, extended grain sizes, few grain boundaries and a low trap-state density. 118 For example, MA + ions are found to be captured inside the framework after the dissolution of MAPbI 3 single crystals in MA gas and form the viscous liquid; the perovskite structure retains to a certain extent even on diluting the viscous liquid in a weak coordination solvent, acetonitrile (ACN).…”

Pyridine Controlled Tin Perovskite Crystallization

“…As confirmed by previous works, the dissolution of the perovskite precursor salts into the solvents leads to the dynamic formation of different colloidal nanoparticles (NPs). 31 , 32 These colloidal NPs are the starting point for the nucleation and growth of perovskite grains during the spin coating process. Their chemical nature and stability are crucial for controlling the quality of the perovskite thin film.…”

Role of solution concentration in formation kinetics of bromide perovskite thin films during spin-coating monitored by optical in situ metrology

“…Nonclassical nucleation and growth mechanisms can explain these phenomena. 50 In addition, 207 Pb NMR measurements on the solution concentration series were performed to investigate the chemical environment of the Pb 2+ ion within the respective solutions. An upeld shi to lower ppm values is observed for increased solution concentration (Fig.…”