Ultrafast electron dynamics in the low-femtosecond regime was evaluated for poly(thiophene) by resonant Auger spectroscopy using the corehole clock method. Sulfur KL 2,3 L 2,3 Auger decay spectra were measured as a function of the photon energy. Remarkable changes developed by tuning the photon energy along the sulfur 1s absorption edge, depending on the nature of the intermediate core excited states. Features characteristics of the Auger Resonant Raman effect were observed. Competition between core hole decay and delocalization of the photoexcited electron was monitored. Branching ratios of Raman (spectator) and normal Auger channels were calculated and electron delocalization times derived.

By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm2 and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units.

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Ultrathin films of poly(3-hexylthiophene) (P3HT) blended with 6,6-phenyl-C61-butyric acid methyl ester (PCBM) were investigated by X-ray absorption spectroscopy (XAS) and resonant Auger spectroscopy (RAS) in the context of the core-hole approach at the sulfur K absorption edge. P3HT:PCBM blend is a well-known system widely used as a bulk heterojunction (BHJ) photoactive layer in organic photovoltaics (OPV). Its morphology, phase separation and ordering of the constituent phases have been proven to significantly affect the performance of the resulting OPV devices. Herein, thermally annealed P3HT:PCBM films at optimum conditions, in terms of power conversion efficiency (PCE) of the resulting fully printed OPV modules (2.22% for 8 cm 2 active area modules), have been proven to be well-ordered films as revealed by the XAS spectra measured at different angles of the incoming photons. Moreover, electron delocalization times were calculated as a function of the excitation energy, resulting in a very low delocalization time in the femtosecond regime.

Ultrathin polymeric films consisting of poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (F8) blended with poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) grown onto PEDOT:PSS/ITO/PET were investigated by X‐ray photoelectron spectroscopy (XPS), depth‐profiling XPS, reflection electron energy loss spectroscopy (REELS) and angle‐dependent X‐ray absorption spectroscopy (XAS) to gain information on the films' electronic, order and interface properties. AFM studies provide valuable information on the films' nanotopographical properties and homogeneity. Spectroscopic ellipsometry and photoluminescence spectroscopy were used also to obtain information on the optoelectronic properties. Well‐ordered films were observed from the XAS analysis, measured at the sulfur K absorption edge. XPS measurements demonstrated that the surface composition of the polymer thin films prepared by a spin‐coating wet‐chemical deposition method matches the expected F8:F8BT blend stoichiometry. The interfacial properties were studied through an argon ion sputtering process coupled to the XPS acquisition, showing an enhancement of oxygen components at the interface. The films' inhomogeneity was verified by AFM images and analysis. We obtained a value of 3.1 eV as the electronic bandgap of the F8:F8BT film from REELS data, whereas analysis of the spectroscopic ellipsometry spectra revealed that the optical bandgap of F8:F8BT has a value of 2.4 eV. A strong green emission was obtained for the produced films, which is in agreement with the expected emission due to the 1:19 ratio of the F8 and F8BT blended polymers. © 2018 Society of Chemical Industry