CHEMICAL ROUTES TO MATERIALS Solution-processed mixed halide CH 3 NH 3 PbI 32x Cl x thin films prepared by repeated dip coating A. M. M. Tanveer Karim 1 , M. S. Hossain 1 , M. K. R. Khan 2, * , M. Kamruzzaman 3 , M. Azizar Rahman 4 , and M. Mozibur Rahman 2 1 Department of Physics, Rajshahi University of Engineering & Technology, Rajshahi 6204, Bangladesh 2 Department of Physics, University of Rajshahi, Rajshahi 6205, Bangladesh 3 Department of Physics, Begum Rokeya University, Rangpur 5400, Bangladesh 4 Department of Physics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh Received: 6 March 2019 Accepted: 1 June 2019 Ó Springer Science+Business Media, LLC, part of Springer Nature 2019 ABSTRACT The mixed halide CH 3 NH 3 PbI 3-x Cl x crystalline thin film has been prepared by two-step solution-processed repeated dip coating method at an ambient atmo- sphere. X-ray diffraction study reveals the presence of tetragonal and cubic phases in deposited film. Raman study confirms the metal halide bond in the inorganic framework and organic CH 3 stretching/bending of C–H bond in CH 3 NH 3 PbI 3-x Cl x perovskite. Scanning electron microscopy shows that cuboid and polyhedral-like crystal grains of 100 nm to 2 lm may find applications in optoelectronics. The perovskite CH 3 NH 3 PbI 3-x Cl x thin film shows high spectral absorption coefficient of the order of 10 6 m -1 . In optical band gap study, we found the coexistence of cubic and tetragonal perovskite phases. The energy band gap is dominated by cubic phase having E g = 2.50 eV over tetragonal phase with band gap E g = 1.67 eV. The room-temperature photoluminescence study confirms band edge, shallow and deep-level emissions. The temperature- dependent cathodoluminescence study shows red, green and ultraviolet emis- sions. The dominating green luminescence evolved for cubic phase at 2.51 eV. The red and ultraviolet emissions are also found for mixed-phase CH 3 NH 3- PbI 3-x Cl x thin film, suitable for preparation of light-emitting devices. Introduction The ability of solution-processed organic–inorganic perovskites CH 3 NH 3 PbX 3 (X = Br, I and Cl) to con- vert visible light into electricity was first discovered in 2006 using CH 3 NH 3 PbBr 3 as a sensitizer on nano- porous TiO 2 in a liquid electrolyte-based dye- sensitized solar cells, but the device power conver- sion efficiency (PCE) was found low [1]. Researchers try to boost up the PCE of solar cells using perovskite nanoparticles or thin film over conventional dyes replacing the halogen site partially but PCE still unsatisfactory. At room temperature, methyl ammo- nium lead tri-iodide (CH 3 NH 3 PbI 3 ) forms a Address correspondence to E-mail: fkrkhan@yahoo.co.uk https://doi.org/10.1007/s10853-019-03740-0 J Mater Sci Chemical routes to materials