Formamidinium Lead Iodide Perovskite Thin Films Formed by Two-Step Sequential Method: Solvent-Morphology Relationship

Thin films made of formamidinium lead iodide (FAPbI(3)) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved alpha-phase formation for all selected solvents. An excessive amount of PbI2 found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2-0.5, 0.2-1 and 2-5 mu m for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications.

Automated summary

This study investigates the correlation between solvent properties and the morphology of thin films made of formamidinium lead iodide (FAPbI(3)) perovskites. Different solvents were used for the two-step sequential deposition method and the resulting thin films were characterized. The results show that the solvent type has an impact on the grain and crystallite size of the films. Thin films fabricated with tert-butanol solvent exhibit very large grain size and preferred crystallite orientation. These findings are significant and interesting for various optoelectronic applications.