"Unlocking the Potential of Transient Absorption Spectroscopy by Examining the Photophysics of Increasingly Complex Systems"
Transient absorption spectroscopy (TAS) provides a powerful tool to examine fundamental photophysical mechanisms of molecules and materials. Photophysical mechanisms describe key dynamics informing design and engineering for materials ranging from single molecules, to thin films through to the fabrication of devices. Unlocking the potential of TAS to inform us about these dynamics requires careful fitting and interpretation of the rich and complex data produced by such experiments. Global lifetime analysis (GLA) is a workhorse fitting technique for TAS data, the proper application of which requires full understanding of its assumptions, advantages and limitations. This thesis discusses the theory and methodology underpinning GLA including when the underlying assumptions break down and how to adapt data analysis in such situations. With these lessons in mind, GLA is then applied to TAS data of increasingly complex systems using careful interpretation to develop complete pictures of the dynamics of the system. Starting with a series of molecular azo dye photoswitches for which analysis of TAS data reveals how photoisomerization behavior is modified via substituents and protonation state. Paired with DFT insight, TAS identifies complex dynamics resulting from protonation. Increasing the complexity, TAS is applied to a series of MoTe2 thin films that decrease in thickness down to a bilayer. Bandgap renormalization is observed to dominate the TAS signal highlighting the strong exciton binding that limits mobility preventing charge injection into a TiO2 layer. Finally, the most complex system, complete Sb2S3 based solar cells are examined. TAS combined with optical modelling reveals changes in dynamics following the addition of a transparent top contact as compared with previous partial device stacks. Proper understanding of the data analysis and experiment demonstrate how TAS, paired with other techniques, can achieve greater physical insight into these systems.