Investigation of Spectral Diffusion due to Static and Dynamic Disorder in Perovskite Thin Films*

Multidimensional coherent spectroscopy (MDCS) is an ultrafast spectroscopy
technique that spreads coherent information across multiple dimensions, resolving features that might overlap in one-dimensional measurements. Both coherent and incoherent
transport, broadening mechanisms, and spectral diffusion can be separated and
clearly measured with MDCS. Additionally, the phase sensitivity of MDCS measurements
allows visualization of the full complex signal field. These attributes
make MDCS ideal for studying complex material systems like
perovskites thin films where cation mixing, ion migration, and inhomogeneous grain
conditions can make spectra difficult to interpret.

Here, we present MDCS spectra from thin films of a mixed-cation perovskite at low temperature. The spectra show inhomogeneously broadened free and defect-bound excitons with a homogeneous dephasing time on the order of 1 ps. The excitons undergo spectral diffusion and relaxation on a much more rapid timescale than has been measured in GaAs quantum wells, increasing the resonance linewidth by a factor of ~3 over one picosecond.