THESIS
2023
1 online resource (xxii, 157 pages) : illustrations (chiefly color)
Abstract
Low-dimensional metal halides have outstanding optoelectronic properties that make
them promising candidates for light-emitting and photovoltaic applications. Recently, lead-free
copper halides are drawing growing attentions due to their high photoluminescence
quantum yields (PLQYs), and the photoluminescence are generally from the recombination of
self-trapped excitons (STEs). However, the factors influencing formation and loss of emissive
species in these materials remains unclear. Additionally, engineering tin halide perovskite into
quasi-2D structures has shown to enhance stability and efficiency of solar cells. Nevertheless,
the excited state characteristics and their relationship to the structural features remain
unexplored.
The thesis presents a comprehensive study on the dynamic...[
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Low-dimensional metal halides have outstanding optoelectronic properties that make
them promising candidates for light-emitting and photovoltaic applications. Recently, lead-free
copper halides are drawing growing attentions due to their high photoluminescence
quantum yields (PLQYs), and the photoluminescence are generally from the recombination of
self-trapped excitons (STEs). However, the factors influencing formation and loss of emissive
species in these materials remains unclear. Additionally, engineering tin halide perovskite into
quasi-2D structures has shown to enhance stability and efficiency of solar cells. Nevertheless,
the excited state characteristics and their relationship to the structural features remain
unexplored.
The thesis presents a comprehensive study on the dynamics and characteristics of STEs in
the low dimensional copper halides, including one-dimensional (1D) CsCu
2I
3 and zero-dimensional
(0D) Cs
3Cu
2X
5 (X=Br, I). The results show that the slower formation of self-trapped
excitons in the 1D structure is due to the larger number of phonons released during
exciton self-trapping, and this process is barrierless. In addition, for the 1D structure, non-radiative
recombination of STEs can occur through the band intersection of STE state and ground state in configuration coordinate diagram, causing an intrinsic loss of PLQY.
Furthermore, 0D Cs
3Cu
2Br
5 shows dual-band emissions from intrinsic STEs and defect-trapped
excitons at low temperature, with no indication of transition observed between them.
Besides, the study of the quasi-2D tin perovskite film using electroabsorption (EA)
spectroscopy reveals that the photoinduced excitons are more ordered and delocalized in the
quasi-2D film compared to its 3D counterpart. The results indicate that the studied quasi-2D
tin perovskite has significantly improved crystal order and reduced defects. The delocalized
excitons and improved structural order contribute to an over 5-fold increase in carrier lifetime
and significantly improved efficiency of the solar cell.
The presented findings shed light on the excited-state characteristics of low-dimensional
metal halides and their impacts on the optoelectronic properties.
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