posted on 2021-05-07, 21:32authored byYeonghun Lee, Hyungjun Kim, Ki-Ha Hong, Kyeongjae Cho
The
excited-state quantum dynamics of the organic cation in hybrid
perovskites are investigated using the time-dependent density functional
theory. The bond fluctuation reveals that the energy relaxation follows
different pathways depending on the chemical bonding characteristics
within the cation molecule, which can fundamentally affect photostability.
For the ammonium-group-containing cations, such as methylammonium
(MA) or ethylammonium (EA), local vibrational modes survive for a
long time. However, as their lowest unoccupied molecular orbitals
(LUMOs) have π* characters, the amidinium-group-containing cations,
such as formamidinium (FA) or guanidinium (GA), efficiently dissipate
deposited energy via chaotic intramolecular vibrational energy redistribution.
The distinct A-site molecules’ dynamics are closely related
to the quantum ergodicity, which can bring enhanced photostability
of FA and GA compared to MA and EA. Our theoretical investigation
reveals the quantum chaos origin of better light stability of FA-based
perovskites and serves as the future research direction of the A-site
engineering for better solar cells and light-emitting devices.