Abstract
In this talk I will present results of the use of X-ray absorption spectroscopy (NEXAFS) and resonant Auger spectroscopy using the core-hole clock (CHC) approach in the investigation of molecular orientation and ultrafast electron dynamics in the low-femtosecond regime for thiophene based-polymers following S K-edge photoexcitation. Remarkable changes developed in the sulfur KL2,3L2,3 Auger decay spectra by tuning the photon energy along the sulfur 1s absorption edge, depending on the nature of the intermediate core excited states. It was possible to disentangle transitions to π* and σ* states not resolved by photoabsorption. Competition between core hole decay and delocalization of the photoexcited electron was monitored and the branching ratio of spectator and normal Auger channels derived. Electron delocalization times in the femtosecond domain were calculated for poly(thiophene) with a value of less than 10 fs on resonance. Results for more complex thiophene-based polymers processed through halogenated and non-halogenated solvents and blended with fullerene/non-fullerene acceptors as well as studies on an ITO-free electrode will be also presented, demonstrating the importance of NEXAFS and the CHC approach to probe molecular ordering and femtosecond electron delocalization dynamics in polymeric thin films for organic photovoltaics.