Abstract
The organic-inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3-xClx 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 CH3NH3PbI3-xClx 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.
Highlights
The organic−inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3−xClx emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV
We focus on thin films fabricated from thermal vapor deposition, which allows for smooth film-formation and high crystalline order, making them very suitable for general device applications.[4]
By scanning the excitation energy across the width of this peak while observing the spectral shape of the PL emission, we establish that the spectral broadening is homogeneous
Summary
The organic−inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3−xClx emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV. Such Stokes shifts are commonly observed in different materials for a variety of reasons including migration of excitations to low-energy sites[25] and lattice relaxation (polaronic effects).[26,27] More remarkable is the apparent presence of additional broadening mechanisms, resulting in the emission line width being almost twice as broad as the spectral width of the absorption onset (56 meV, determined as the FWHM of the derivative of the absorption edge; see Supporting Information).
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