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Solar cells based on kesterite-type Cu2ZnSnS4 (CZTS) thin films were fabricated using a chemical route to prepare the CZTS films, consisting in sequential deposition of Cu2SnS3 (CTS) and ZnS thin films followed by annealing at 550 • C in nitrogen atmosphere. The CTS compound was prepared in a one-step process using a novel chemical procedure consisting of simultaneous precipitation of Cu2S and SnS2 performed by diffusion membranes assisted CBD (chemical bath deposition) technique. Diffusion membranes were used to optimize the kinetic growth through a moderate control of release of metal ions into the work solution. As the conditions for the formation in one step of the Cu2SnS3 compound have not yet been reported in literature, special emphasis was put on finding the parameters that allow growing the Cu2SnS3 thin films by simultaneous precipitation of Cu2S and SnS2. For that, we propose a methodology that includes numerical solution of the equilibrium equations that were established through a study of the chemical equilibrium of the system SnCl2, Na3C6H5O7·2H2O, CuCl2 and Na2S2O3·5H2O. The formation of thin films of CTS and CZTS free of secondary phases grown with a stoichiometry close to that corresponding to the Cu2SnS3 and Cu2ZnSnS4 phases, was verified through measurements of X-ray diffraction (XRD) and Raman spectroscopy. Solar cell with an efficiency of 4.2%, short circuit current of 16.2 mA/cm 2 and open-circuit voltage of 0.49 V was obtained.

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Herein, mixed CH3NH3PbI3/(CH3NH3)2PbI2(SCN)2 (MAPI/MAPSI) thin films are synthesized. Arising from X‐ray diffraction measurements, the composite material is found to be consisting of two crystalline domains, one for each MAPI and MAPSI constitutent materials. Optical analysis from diffuse reflectance spectroscopy shows optical onsets for both the MAPI and MAPSI domains, making the fabricated material an interesting one for multi‐bandgap absorber composite for solar cell devices. Scanning electron microscopy studies yield a noticeable morphology enhancement for the MAPI/MAPSI films when treated with a toluene dripping technique, and then show films with uniform, compact grains in contrast to an initial porous, dendritic growth morphology for the untreated films. A question about the actual geometry for the thiocyanate anions in MAPSI is answered as being of axial configuration around the Pb cation, enlightened by the results of state‐of‐the‐art density functional theory computational modelling within the framework of the Quantum Espresso software package suite, also in‐depth studying of the MAPSI structure through bond indicators such as crystal orbital Hamilton population, non‐covalent interactions analysis, and electron localization function.

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