Homogeneous Emission Line Broadening in the Organo Lead Halide Perovskite CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i>

Abstract

The organic–inorganic hybrid perovskites methylammonium lead iodide (CH₃NH₃PbI₃) and the partially chlorine-substituted mixed halide CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV. However, the nature of the radiative decay channels behind the observed emission and, in particular, the spectral broadening mechanisms are still unclear. Here we investigate these processes for high-quality vapor-deposited films of CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> using time- and excitation-energy dependent photoluminescence spectroscopy. We show that the PL spectrum is homogenously broadened with a line width of 103 meV most likely as a consequence of phonon coupling effects. Further analysis reveals that defects or trap states play a minor role in radiative decay channels. In terms of possible lasing applications, the emission spectrum of the perovskite is sufficiently broad to have potential for amplification of light pulses below 100 fs pulse duration