Size, Ligand, and Defect-Dependent Electron-Phonon Coupling in Chalcogenide and Perovskite Nanocrystals and Its Impact on Luminescence Line Widths

The systematic study of electron-phonon coupling in nanocrystals (NC) via first-principles methods has been limited by the large system sizes presented by the NCs. Here, we present a method to extract electron-phonon coupling strengths from ab initio Molecular Dynamics simulations that is computationally less demanding. We use this method to investigate how electron-phonon coupling strengths depend on NC size, ligands, and defects for the model system of PbS NCs and also demonstrate its general applicability by leveraging the approach to compute electron-phonon coupling strengths in CdSe and CsPbI3 NCs. The strong coupling of phonons to interband transitions in all NCs imposes fundamental limits to emission line widths. Our results indicate that coupling to localized vibrations stemming from undercoordinated atoms on the surface of the NCs contribute significantly to line width broadening and help to explain the experimentally observed trend that homogeneous line widths decrease with increasing NC size. Finally, we also demonstrate that mild surface defects on the NCs, which do not impact the ground state electronic structure of the NC, can dramatically increase radiative line widths.