Excitons in Perovskites Microscopic Modelling of Exciton Spectra in Perovskites and Exciton-Phonon Coupling
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Typ
Examensarbete för masterexamen
Program
Publicerad
2022
Författare
Joki, Ambjörn
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Perovskites are interesting materials due to their special optoelectronic properties —
properties already being used in photovoltaics and potentially in future light-emitters.
Since perovskites exhibit strongly bound excitons, the excitons are, often still at
room temperature, crucial to consider. In this work a model aimed at describing
the excitonic landscape in 2D and 3D perovskites has been developed. The model
includes the exchange interaction giving rise to an exciton fine structure consisting of
optically active and inactive exciton states, the latter with lower energy. The model
is further extended by inclusion of a magnetic field, necessary in experimental setups
to probe the inactive states. The developed model captures the qualitative excitonic
aspects of 3D perovskites predicting three optically active states and one inactive,
but is incomplete in the 2D case predicting two active and two inactive states. The
incompleteness is probably related to the treatment of the confined direction in 2D.
Further, the exciton phonon scattering between active and inactive states is modelled.
For applications the phonon scattering is important since high scattering rates will
transfer many excitons from optically active states to the inactive one with lower
energy, reducing the light emission. However, indications of a phonon bottleneck
— reduced scattering rate — have been observed. Assuming spin conservation, the
phonon scattering between active and non-active states is found to be non-existing
— thus further confirming the phonon bottleneck. The model contributes to better
microscopic understanding of the exciton-phonon coupling in perovskites.
Beskrivning
Ämne/nyckelord
bright excitons , dark excitons , phonon-exciton scattering , phononbottlenecks , perovskites , magnetic field