Organic semiconducting films continue to garner interest due to their ease of fabrication for potential application in flexible electronics such as OLEDs and solar cells. Solution processed deposition and post-fabrication methods, such as thermal annealing, greatly influence the structure of molecular aggregates in these films. Since electronic structure and excited state dynamics, both influenced by aggregate structure, determine the utility of a material in an organic device, it is valuable to understand how these photophysical properties evolve throughout the fabrication process. Transient absorption (TA) spectroscopy is a pump-probe technique that can measure the excited state dynamics of organic materials, but, in typical implementations, many minutes to hours are needed to measure a sample. Typically, the time delay between pump and probe pulses is generated by changing the pathlength of one of the two beams by moving a mirror mounted on a motorized translation stage. Data is collected at several positions until a reasonable signal-to-noise ratio is acquired, hence the lengthy measurement time, which precludes measurements during solution deposition or thermal annealing. We have developed a broadband single-shot transient absorption (SSTA) instrument that employs a spatially encoded time delay between the pump and probe pulses. This enables us to collect a 60-ps transient spectrum in a few seconds. We describe the experimental setup and calibration methods that validate this technique and present broadband SSTA measurements performed in situ during molecular aggregation and thermal annealing of organic films of electron donors and acceptors. This work explores the transitionary stages during film fabrication and will give insight into the influence of processing parameters on excited state dynamics.

<i>In situ</i> broadband single-shot transient absorption measurements of organic films

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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In situ broadband single-shot transient absorption measurements of organic films