Citation: Echeverría-Arrondo, C.; Alvarez, A.O.; Masi, S.; Fabregat-Santiago, F.; Porta, F.A.L. Electronic, Structural, Optical, and Electrical Properties of CsPbX 3 Powders (X = Cl, Br, and I) Prepared Using a Surfactant-Free Hydrothermal Approach. Nanomanufacturing 2023, 3, 217–227. https://doi.org/10.3390/ nanomanufacturing3020013 Academic Editor: Riccardo Frisenda Received: 19 January 2023 Revised: 3 May 2023 Accepted: 5 May 2023 Published: 19 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Electronic, Structural, Optical, and Electrical Properties of CsPbX 3 Powders (X = Cl, Br, and I) Prepared Using a Surfactant-Free Hydrothermal Approach Carlos Echeverría-Arrondo 1 , Agustin O. Alvarez 1 , Sofia Masi 1 , Francisco Fabregat-Santiago 1 and Felipe A. La Porta 1,2,3, * 1 Institute of Advanced Materials (INAM), Universitat Jaume I, Av. Sos Baynat, s/n, 12006 Castellón, Spain 2 Nanotechnology and Computational Chemistry Laboratory (NANOQC), Federal Technological University of Paraná, Avenida dos Pioneiros 3131, Londrina 86036-370, PR, Brazil 3 Post-Graduation Program in Chemistry, State University of Londrina, Londrina 86057-970, PR, Brazil * Correspondence: felipelaporta@utfpr.edu.br Abstract: Recently, several strategies have been adopted for the cesium lead halide, CsPbX 3 (X = Cl, Br, and/or I), crystal growth with a perovskite-type structure, paving the way for the further devel- opment of innovative optoelectronic and photovoltaic applications. The optoelectronic properties of advanced materials are controlled, in principle, by effects of morphology, particle size, structure, and composition, as well as imperfections in these parameters. Herein, we report a detailed investi- gation, using theoretical and experimental approaches to evaluate the structural, electronic, optical, and electrical properties of CsPbX 3 microcrystals. The microcrystals are synthesized successfully using the hydrothermal method without surfactants. This synthetic approach also offers an easy upscaling for perovskite-related material synthesis from low-cost precursors. Lastly, in this direction, we believe that deeper mechanistic studies, based on the synergy between theory and practice, can guide the discovery and development of new advanced materials with highly tailored properties for applications in optoelectronic devices, as well as other emergent technologies. Keywords: hydrothermal processing; DFT calculations; cesium lead halide perovskites; crystals 1. Introduction Due to their extraordinary physical properties, lead halide perovskites have attracted noteworthy interest in emerging technologies (photovoltaic, sensor, optoelectronic, etc.) [1–4]. Notably, lead halide perovskite structures are found in related compounds with the general formula APbX 3 , usually consisting of a ternary combination of corner-sharing [PbX 6 ] polyhedral clusters in the lattice with an organic or inorganic monovalent cation A, such as methylammonium (MA), formamidinium (FA), or cesium (Cs), with the X site being primarily a monovalent halide (i.e., Cl, Br, I, or a combination thereof) anion [3]. It is well known that APbX 3 -related compounds can adopt four phases (a-cubic, b-tetragonal, and g- and d-orthorhombic) depending on the tilt and rotation of the [PbX 6 ] polyhedral clusters in the lattice [4–7]. For this reason, the formation mechanisms of the most likely crystal structure of lead halide perovskites have been widely studied in the literature from the perspective of the Goldschmidt tolerance factor, t, defined as t = (rA + rX)/[sqrt(2)(rB + rX)], where rA, rB, and rX are the ionic radii of the individual A, B, and X species, respectively [7]. Hence, according to this empirical relation, when t ranges from 0.7 to 1, stable lead halide perovskites can generally be formed [3,8,9]. Such materials have a high power conversion efficiency (PCE) with a record of 25.8% (certified 25.5%), which has been achieved over the last decade [10]. Despite this significant PCE result, however, the stability of APbX 3 -based devices is still weak with regard to Nanomanufacturing 2023, 3, 217–227. https://doi.org/10.3390/nanomanufacturing3020013 https://www.mdpi.com/journal/nanomanufacturing