Structural and Optical Properties of Two-Step Dip-Coated CH3NH3PbI3 Films Based on Underlying Dip-Coated PbI2 Films

Thin films of methylammonium lead iodide (MAPbI3) were deposited on glass slides under various preparation conditions by a two-step dip-coating method, using dip-coated lead iodide (PbI2) thin films as the underlying layer. The dip-coating method used involved immersion of a slowly rotating substrate in the required solution. The PbI2 film was immersed into methylammonium iodide (MAI) solution in 2-propanol for 10–60 min. The MAPbI3 films were thermally annealed at 85 °C for 10–30 min. Fundamental properties of the annealed MAPbI3 films were studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible spectrophotometry. The XRD patterns and SEM micrographs revealed single tetragonal-phase structure, with diffraction peaks became intense and narrow with increasing dipping times and upon thermal annealing. Transmittance spectra of these MAPbI3 film/glass systems declined steeply near 780nm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$780\mathrm{ nm}$$\end{document}, equivalent to a bandgap energy of 1.55eV\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.55\mathrm{ eV}$$\end{document}, assigned to the MAPbI3 with optical absorption coefficient of 105cm-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${10}^{5} {\mathrm{cm}}^{-1}$$\end{document}.