Search

In this work, we present the effect of the treatment of PbI 2 thin films with dimethyl sulfoxide (DMSO) vapor on the final characteristics and properties of CH 3 NH 3 PbI 3– x Cl x perovskite synthesized from a three-step approach. This is an additional step, thus, it changes the previous approach to a four-step sequence, which, for the present research, consists in the following: (1) chemical solution deposition of PbS thin films over glass substrates; (2) chemical transformation of the deposited PbS thin films into PbI 2 by means of a gas–solid reaction with iodine vapor; (3) surface treatment of the synthesized PbI 2 thin films with DMSO vapor, being this step the driving force of the present research; and (4) chemical transformation of the DMSO-treated PbI 2 thin films into CH 3 NH 3 PbI 3– x Cl x perovskite films by means of a liquid–solid reaction with a spin-coated solution mix of methylammonium iodide/chloride. We particularly present here the effect of four exposure times to DMSO vapor (5, 10, 15, and 20 min), which were compared against an untreated reference. The thin films of all the synthesized materials were uniform and strongly adhered to the glass substrate. The PbI 2 and perovskite samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) and fluorescence spectroscopies. It was observed that all the DMSO-treated PbI 2 films present pores and, thus, show a decrease of transmittance. They also lead to subsequent perovskite samples that present blurred grain boundaries, which are less pronounced in comparison to the reference perovskite, which was synthesized from PbI 2 with no DMSO treatment. This resultant morphology, translated in a better continuity of the perovskite material, was attributed as the cause of the increased photocurrent and responsivity of the photodetector fabricated from perovskite synthesized from DMSO-treated PbI 2 film, as compared with the photodetector fabricated with the reference perovskite. Therefore, the treatment of PbI 2 thin films with DMSO vapor is beneficial for improving the photodetector characteristics of CH 3 NH 3 PbI 3– x Cl x perovskites. Image 1 • Solution/vapor/solution approach to prepare CH 3 NH 3 PbI 3– x Cl x perovskite films. • PbI 2 surface engineering with DMSO vapor to increase porosity. • Porous PbI 2 leads perovskite with blurred grain boundaries. [ABSTRACT FROM AUTHOR]

A low-cost, simple, reproducible, and industry-scalable three-step approach that permits full control over film growth is used to prepare CH 3 NH 3 PbI 3– x Cl x 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 PbI 2 by means of a gas–solid reaction with iodine vapor; and (3) the synthesis of CH 3 NH 3 PbI 3– x Cl x perovskite by exposing the obtained PbI 2 films to a CH 3 NH 3 I/CH 3 NH 3 Cl vapor mix. The materials obtained at each step, them being PbS, PbI 2 , and CH 3 NH 3 PbI 3– x Cl x , 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 PbI 2 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. Image 105025 • Solution/vapor/vapor three-step approach to prepare CH 3 NH 3 PbI 3– x Cl x perovskite films. • Chemical bath deposition and (2) iodine and (3) methylammonium vapor reactions. • The whole route is simple, low-cost, reproducible, and compatible with the industry. • Obtained perovskite films are compact, homogeneous, strong-adhered, and crystalline. • Preliminary perovskite-based photodetector device is fabricated and evaluated. [ABSTRACT FROM AUTHOR]

Abstract The chemical solution deposition of Mg(OH) 2 thin films on glass substrates and their transformation to MgO by annealing in air is presented. The chemical solution deposition consists of a chemical reaction employing an aqueous solution composed of magnesium sulfate, triethanolamine, ammonium hydroxide, and ammonium chloride. The as-deposited films were annealed at different temperatures ranging from 325 to 500 °C to identify the Mg(OH) 2 -to-MgO transition temperature, which resulted to be around 375 °C. Annealing the as-deposited Mg(OH) 2 films at 500 °C results in homogeneous MgO thin films. The properties of the Mg(OH) 2 and MgO thin films were analyzed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and by circular transmission line model. Results by X-ray diffraction show that the as-deposited thin films have a brucite structure (Mg(OH) 2), that transforms into the periclase phase (MgO) after annealing at 500 °C. For the as-deposited Mg(OH) 2 thin film, a nanowall surface morphology is found; this morphology is maintained after the annealing to obtain MgO, which occurred with the evident formation of pores on the nanowall surface. The assessed chemical composition from X-ray photoelectron spectroscopy yields Mg 0.36 O 0.64 (O/Mg ratio of 1.8) for the as-deposited Mg(OH) 2 film, where the expected stoichiometric composition is Mg 0.33 O 0.67 (O/Mg ratio of 2.0); the same assessment yields Mg 0.60 O 0.40 (O/Mg ratio of 0.7) for the annealed thin film, which indicates the obtainment of a MgO material with oxygen vacancies, given the deviation from the stoichiometric composition of Mg 0.50 O 0.50 (O/Mg ratio of 1.0). These results confirm the deposition of Mg(OH) 2 films and the obtainment of MgO after the heat-treatment. The energy band gap of the films is found to be 4.64 and 5.10 eV for the as-deposited and the film annealed at 500 °C, respectively. The resistivity of both Mg(OH) 2 and MgO thin films lies around 108 Ω·cm. [ABSTRACT FROM AUTHOR]