Structural, Optical, and Chemical Characteristics of High-Quality PbI₂ Thin Films via Chemical Solution Deposition with Thermal Annealing

Herein, a synthesis method for obtaining lead iodide through chemical bath deposition, a type of chemical solution deposition without the use of organic solvents, is presented; the process consists of three stages. In the first stage, tin hydroxide films are produced which act as a seed layer allowing for a better adherence of the film that is to be deposited. The second stage consists of the synthesis of the lead iodide films. Finally, annealing is done (100, 150, and 200 & DEG;C) with the purpose of promoting the polytypic transitions of the material and to study the effect of these structures on the properties of the material. Assessment of the structural and optical properties of the films is done by means of scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, Raman spectroscopy, and transmission electron microscopy, where a direct influence of the annealing in the induction of polytypes is observed. The resultant PbI2 films have a large-area coverage across the substrate, wide-bandgap (2.38 eV), and a structure that belongs to the 2H and 4H polytypes. Hence, it is suggested from these results that the chemically deposited PbI2 thin films are promising candidates for large-area optoelectronic applications.