Understanding Method-Dependent Differences in Urbach Energies in Halide Perovskites
Christina Witt, Konstantin Schötz, Anna Köhler, Fabian Panzer
Abstract
The Urbach energy as a measure of energetic disorder is an important characteristic of semiconductors to evaluate their optoelectronic functionality. However, discrepancies occur in Urbach energy values E U determined via different measurement and analysis methods, whose origin of a profound understanding is still missing. To reliably analyze the origin of such discrepancies, we recorded quasi-simultaneously temperature-dependent absorption and photoluminescence (PL) spectra of halide perovskite (MAPbI 3 ) thin-film and single-crystal samples. Performing profound Urbach analyses in an extended energy range down to 0.2 eV below the bandgap, we find energy-range-dependent exaggeration effects on Urbach energy values to be only present in the near bandgap region (∼0.02 eV below the bandgap), where non-Urbach absorption states start to contribute. Besides that, generally lower E U values and a lower temperature-dependence of E U are obtained from PL than from absorption, which originates from the sensitivity of PL for sites with lower energetic disorder and/or higher phonon energies in the excited-state geometry. Thus, our work is sensitized to proper interpretation and comparison of E U values and contributes to developing a more fundamental understanding of semiconductor materials.