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-x)PbI3 (FA(x)MA(1-x)PbI(3)) (x = 0.8, 0.6, 0.4, 0.2) perovskite nanostructures through a simple solution method. The morphology and crystal structure of the FA(x)MA(1-x)PbI(3) nanostructures are measured by field emission scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The temperature-dependent photoluminescence (PL) of FA(x)MA(1-x)PbI(3) 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 FA(x)MA(1-x)PbI(3) 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 similar to 25 meV was fitted from the absorption spectra. These results on optical properties indicate the advantage of FA(x)MA(1-x)PbI(3) in solar cell devices.