Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals

Nonradiative processes limit optoelectronic functionality of nanocrystals and curb their device performance. Nevertheless, the dynamic structural origins of nonradiative relaxations in such materials are not understood. Here, femtosecond electron diffraction measurements corroborated by atomistic simulations uncover transient lattice deformations accompanying radiationless electronic processes in colloidal semiconductor nanocrystals. Investigation of the excitation energy dependence in a core/shell system shows that hot carriers created by a photon energy considerably larger than the bandgap induce structural distortions at nanocrystal surfaces on few picosecond timescales associated with the localization of trapped holes. On the other hand, carriers created by a photon energy close to the bandgap of the core in the same system result in transient lattice heating that occurs on a much longer 200 picosecond timescale, dominated by an Auger heating mechanism. Elucidation of the structural deformations associated with the surface trapping of hot holes provides atomic-scale insights into the mechanisms deteriorating optoelectronic performance and a pathway towards minimizing these losses in nanocrystal devices. Charge trapping can lead to severe nonradiative losses in colloidal semiconductor nanocrystals (NCs). The authors report femtosecond electron diffraction measurements on photoexcited NCs to reveal atomic-scale insights into how localization of charges at trap sites induce surface deformations.

Automated summary

A study reveals that transient lattice deformations are observed in photoexcited nanocrystals, with surface deformations induced by localized charges at trap sites. The structural distortions are influenced by the excitation energy, showing different behaviors when the photon energy is above or close to the bandgap.