Understanding organic materials formation using in situ transient absorption spectroscopy*

The electronic structure and exciton dynamics of the molecules and polymers that form the active layer in organic electronic devices can change dramatically during the formation and processing of thin films. During solution deposition solvent vaporizes, forcing molecules and polymers to aggregate and become electronically coupled. Thermal annealing may further change the conformation of polymers and relative intermolecular arrangement of small molecules. This can dramatically change the exciton dynamics and thus the suitability of the material for electronic devices. The exciton dynamics of organic molecules and polymers can be measured using transient absorption spectroscopy. However, the progression of exciton dynamics during film formation and processing is unknown since measurements typically cannot be performed quickly enough to collect accurate transient absorption spectra while the systems are changing. The exciton dynamics of evolving material systems can be measured by increasing the speed of data collection. In this work, a single-shot transient absorption spectroscopy technique is used that can measure transient spectra with up to a 60 ps pump-probe time delay in mere seconds. The exciton dynamics of an organic semiconducting system is revealed during the formation of an organic film. These measurements provide a new way to understand the mechanism of organic film formation and the impact of these complex processes on excited state dynamics.