Two-dimensional, organic-inorganic hybrid perovskites (2DHPs) are stoichiometric compounds composed of alternating sheets of corner-sharing, metal-halide octahedra and organoammonium cationic layers. We study 2DHPs containing single lead iodide layers separated by intervening substituted, phenethylammonium (PEA) cations with the chemical structure (x-PEA)2PbI4, where x=F, Cl, Br, or CH3. These 2DHPs form type-I heterojunctions in which excitons and carriers are strongly confined to the lead halide layers with exciton binding energies &gt; 150 meV. We use x-ray diffraction and variable-temperature steady-state and time-resolved absorption and photoluminescence (PL) measurements to uncover the correlation between their structure and photophysical properties. (PEA)2PbI4 excitonic absorption and PL spectra at 15 K show splittings into regularly spaced resonances every 40-46 meV. Anti-Stokes hot exciton PL is observed at the same energy as the optical absorption resonances. Replacing a single atom in the para position of the PEA-cation phenyl group increases its length and therefore the interlayer spacing, but leaves the cross-sectional area unchanged and results in structurally similar metal halide frameworks. As the cation length increases, the absorption spectra broaden and blueshift, but the PL spectra remain invariant. Substitution in the ortho position with progressively larger cations increasingly distorts and strains the inorganic framework. Ortho substitutions change the number of and spacing between the discrete excitonic resonances and increase the hot exciton PL by &gt;10X. By correlating the atomic substitutions on the cation with changes in the excitonic structure, we show that the origin of the discrete excitonic resonances is consistent with a vibronic progression caused by strong exciton-phonon coupling to a phonon on the organic cation. The properties of 2DHPs can be tailored by the selection of the cation without directly modifying the inorganic framework.

Hot exciton dynamics in two-dimensional organic-inorganic hybrid perovskites

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.