Temperature-dependent photoluminescence properties of mixed-cation methylammonium–formamidium lead iodide [HC(NH2)2]x[CH3NH3]1−xPbI3 perovskite nanostructures

In this paper, we synthesized mixed-cation [HC(NH2)2]x[CH3NH3]1−xPbI3 (FAxMA1−xPbI3) (x = 0.8, 0.6, 0.4, 0.2) perovskite nanostructures through a simple solution method. The morphology and crystal structure of the FAxMA1−xPbI3 nanostructures are measured by field emission scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The temperature-dependent photoluminescence (PL) of FAxMA1−xPbI3 nanostructures is investigated; the integrated PL intensity exhibits an exponential decrease with the increase of temperature. An abnormal redshift of the center PL emission wavelength due to orthorhombic–tetragonal phase transition in the transitional temperature region around 150 K is observed from the temperature-dependent PL; the center PL emission wavelength shows continuous blue-shift in the pure orthorhombic phase and tetragonal phase. In addition, the exciton binding energy of FAxMA1−xPbI3 nanostructures was obtained by analysing the PL intensity decay. The exciton binding energy decreases when the FA/MA ratio approaches 1 : 1. The low Urbach energy of ∼25 meV was fitted from the absorption spectra. These results on optical properties indicate the advantage of FAxMA1−xPbI3 in solar cell devices.