Synthesis of CH3NH3PbI3-xClx perovskite by the three-step route consisting of chemical solution deposition followed by gas-solid reaction transformations: Film quality and photodetector performance evaluation

A low-cost, simple, reproducible, and industry-scalable three-step approach that permits full control over film growth is used to prepare CH3NH3PbI3-xClx perovskite films and the advantages of the process is demonstrated with the evidence presented for each reaction step. The whole route consists in (1) the chemical solution deposition of PbS thin films on a desired substrate; (2) the transformation of the PbS films to PbI2 by means of a gas-solid reaction with iodine vapor; and (3) the synthesis of CH3NH3PbI3-xClx perovskite by exposing the obtained PbI2 films to a CH3NH3I/CH3NH3Cl vapor mix. The materials obtained at each step, them being PbS, PbI2, and CH3NH3PbI3-xClx were qualitatively evaluated regarding homogeneity and adhesion, and studied by scanning electron microscopy, X-ray photoelectron spectroscopy (including a detailed analysis of the X-ray photoelectron spectra), X-ray diffraction, and ultraviolet-visible spectroscopy. These tests and techniques demonstrate the successful obtainment of the desired material at each step of the presented route and the formation of films with strong adhesion to the glass substrate. Particularly, the inexpensive and simple synthesis of PbI2 by an industry-compatible sequence is confirmed. Perovskite obtained by this process as an end-product was crystalline and, as confirmed by fluorescence spectroscopy, presented an energy bandgap of 1.61 eV; furthermore, the perovskite film was homogeneous and uniformly coated the substrate surface showing no pinholes. Preliminary results on the application of this perovskite in a photodetector device are also included.