Ultrafast photophysics of organohalide perovskites by transient extreme ultraviolet spectroscopy

Tabletop transient extreme ultraviolet spectroscopy (tXUV) offers an unprecedented opportunity to understand nonequilibrium photophysical properties of complex semiconductor materials down to the femtoseconds scale. Element and carrier specificity, combined with sub-femtosecond time resolution of the technique provides a twofold opportunity: first, the table-top setup allows for flexible instrumentation and data processing method development to the broader materials chemistry community. Second, fundamental insights on ultrafast photophysics enable the development of optoelectronic devices with precisely controlled properties. The tXUV experiments presented in this thesis provide fundamental understanding of energy loss mechanisms in hybrid organic inorganic perovskites after photoexcitation. The goal of the first research effort on methylammonium lead bromide is to simultaneously uncover carrier-specific photophysical processes in femtosecond to picosecond timescales. The second research effort focuses on comparing ultrafast dynamics of two prototypical layered perovskites with different organic linkers. Both studies are motivated by the potential applications of these materials in next generation optoelectronic devices. Our experiments on ultrafast hole cooling dynamics in MAPbBr3 showed that holes are hotter than electrons. These results highlight that holes in 3D perovskites may behave differently than electrons, raising more questions on their applicability in hot-carrier photovoltaics. We also developed a data processing method to extract band shifts of excited state MAPbBr3 from tXUV spectra. Carrier-induced band shift values can be used to extract carrier effective mass, thus indirectly mapping polaronic distortions in excited state. Next, we presented results on ultrafast cation independent hole recombination dynamics in two prototypical layered perovskite structures with aromatic and aliphatic linkers. First, we showed how static XUV spectroscopy can probe the changes in electronic structure with structural tuning. We mapped comparable hole recombination dynamics for layered perovskite samples with different cations. Rapid Auger recombination in layered perovskites reduces their photoluminescence quantum yield, and this study reaffirms the need for optimizing linker engineering to minimize Auger effects. In summary, this thesis demonstrates a combination of time-resolved spectroscopic techniques that provide a fundamental understanding of photophysical properties of emerging halide perovskite materials.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Sharma, Aastha

Contributors dc:contributor

• Vura-Weis, Josh
• Schleife, André
• Murphy, Catherine J
• Nuzzo, Ralph G

• ultrafast spectroscopy
• organohalide perovskites
• extreme ultraviolet spectroscopy
• semiconductor photophysics
• carrier dynamics

Statement dc:rights

• Copyright 2022 Aastha Sharma

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/116087

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F116087