Lead iodide (PbI 2 ) thin films are interesting semiconductor materials arranged in quasi 2D layers, [1] that have an optical bandgap near the ultraviolet (E g = 2.4 eV) spectrum and are composed of atoms with a high atomic mass. [2,3] These characteristics of PbI 2 allow its use in diverse applications, [4][5][6][7][8] with a recent interest in large-area visible, X-ray, and γ-ray radiation detectors. [2,9] Additionally, PbI 2 thin films are excellent precursors in the chemical synthesis of lead halide perovskite CH 3 NH 3 PbI 3 (MAPI) thin films, [10][11][12] which are photovoltaic materials of great importance. However, whether PbI 2 can be used as a high-performance optoelectronic material or efficient chemical precursor, strongly depends on achieving favorable structural properties. [3,[12][13][14] Moreover, the understanding of how the different deposition conditions affect the multiple stacking conformations that the compact PbI 2 layers take [15] is challenging. Different structural configurations known as polytypes [16] can be achieved but are difficult to reproduce, [3] and can lead to diverse microstructures, [17][18][19] that in turn produce varying optical and electrical properties.Different polytypes can be obtained according to the annealing conditions [20] and the implemented synthesis methodology. [21] Diverse previous studies have reported the synthesis of PbI 2 employing thermal evaporation, physical vapor deposition, laser ablation, atomic layer deposition, spray pyrolysis, and spin-coating with favorable crystalline properties. [12][13][14]22,23] The literature shows that the most common polytype is the 2H, albeit the 4H and 12R polytypes have been reported [24,25] at annealing treatments of 150 and 170 °C, respectively. Achieving the 4H and 12R polytypes may improve the optoelectronic properties in large-area radiation sensors, as well as favoring the quality and stability of perovskite thin films. Thus, the use of PbI 2 thin films in such purposes requires the examination of the structural properties at specified synthesis parameters.Therefore, in this work, we explore the synthesis of PbI 2 thin films via chemical bath deposition (CBD), a technique that has not been extensively studied for the deposition of PbI 2 thin films, only few reports exist in the literature. [3,26] CBD, when done correctly, enables the deposition of uniform, homogeneous, and large-area thin films that are strongly adhered to almost any kind of substrate. This technique does not require complex infrastructure, ergo it is low cost and easy to implement, and has been proven successful for the synthesis of numerous metal iodide thin films. [27][28][29][30] However, achieving good-quality films is complicated, because it requires fine tuning of the chemical formulation (reaction solution), as shown by the work of Kariper [3] where the structure and optical properties of the PbI 2 thin films are significantly influenced by the pH of the reaction solution.