Publication date: 22nd July 2026
Electron-phonon coupling plays a central role in determining the optoelectronic response of two-dimensional layered perovskites, yet the specific lattice degrees of freedom that mediate this coupling remain difficult to identify. This challenge arises from the structural complexity of hybrid perovskites, where mechanically coupled organic and inorganic sublattices form large, anharmonic unit cells with many closely spaced vibrational modes. As a result, low-frequency Raman modes are often assigned to inorganic framework motion, while the role of the organic spacer layer is treated as secondary.
Here we combine vibrational spectroscopy, lattice engineering and first-principles analysis to resolve the hybrid lattice dynamics of layered perovskites. We show that the normal modes are intrinsically organic-inorganic in character and cannot be separated into purely molecular or framework vibrations. This hybridization persists even below 50 cm-1, a spectral region conventionally associated with octahedral tilts and inorganic lattice distortions. Chemical substitution of the organic spacer selectively modifies these low-frequency modes, demonstrating that the organic sublattice provides an active handle for tuning the vibrational landscape.
We then examine the lattice response under above-bandgap excitation and identify spectroscopic signatures of polaronic distortion [1]. The excited-state spectra reveal that polaron formation is governed by hybrid vibrational coordinates involving both the inorganic framework and the organic spacer layer. In particular, the polaronic response is consistent with a vibronic mechanism in which a Franck-Condon progression of a Jahn-Teller-like framework distortion couples to a hybrid soft mode through Herzberg-Teller interactions. These results show that the organic sublattice is not merely a passive structural spacer but actively participates in stabilizing the photoinduced polaronic state.
By linking lattice hybridization, chemical control and excited-state vibrational response, this work establishes hybrid phonon engineering as a route to tune polaron formation in two-dimensional perovskites. More broadly, it highlights the need to resolve lattice dynamics under operating conditions in order to understand and design the photophysical properties of hybrid optoelectronic materials.
This work has been partially funded by the National Science Centre Poland within the OPUS program Grant No. 2023/51/B/ST5/02908
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