Time-resolved EPR for probing ordering in conjugated polymers and primary processes of charge generation in organic electronic devices

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Organic semiconductors are used in a large number of applications ranging from light-emitting diodes (OLEDs) and transistors (OFETs) to solar cells (OSCs). Their advantage over conventional inorganic semiconductors is the low-cost and nearly endless flexibility in tailoring the molecules used. Generation, separation, and transport of charges are crucial aspects that need further investigation to develop efficient organic electronics. Morphology of the involved polymers is one of the most crucial aspects for the efficiency of organic electronic devices due to the existing strong structure-function relationship. Electron paramagnetic resonance (EPR) spectroscopy is nearly ideally suited to investigate conjugated polymers used for organic electronics, as most of the light-induced states are paramagnetic and can therefore be detected.The focus of this project is on investigating morphology and ordering in conjugated polymers and light-induced primary processes in organic electronic devices by time-resolved EPR spectroscopy. The microscopic processes are correlated with both, the morphology of the polymers and the macroscopic device efficiency. Due to the strong structure-function relationship, it is crucially important to control the sample morphology. Only if it is comparable to that in organic electronic devices, spectroscopic results can be correlated to device characteristics.In a systematic approach, the materials used for organic electronics will be investigated spectroscopically - starting out with the building blocks and continuing via oligo- and polymers to the blends of donor and acceptors materials used in the actual devices. To correlate morphology, microscopic processes and macroscopic device efficiency, an EPR setup to investigate whole organic electronic devices (OFETs, OSCs) will be built. Analysis of spin-polarised EPR spectra will be facilitated by developing an easy-to-use framework of simulation programs covering the different scenarios.