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In situ measurement of a polymer solar cell using micro grazing incidence small angle X-ray scattering (μGISAXS) and current-voltage tracking is demonstrated. While measuring electric characteristics under illumination, morphological changes are probed by μGISAXS. The X-ray beam (green) impinges on the photo active layer with a shallow angle and scatters on a 2d detector. Degradation is explained by the ongoing nanomorphological changes observed.

Cosolvent addition of glycerol (G) and the use of the cosolvent ethylene glycol (EG) increase the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films to values on the order of indium tin oxide conductivity. The underlying morphological changes are probed via scanning electron microscopy as well as advanced scattering techniques microfocused grazing incidence small-and wide-angle Xray scattering. The enhancement in conductivity is ascribed to fundamental morphological changes and molecular reorientation within crystalline domains. Thereby, the conductivity enhancement is directly correlated to domain ruptures toward smaller and more densely packed PEDOT domains together with an enhanced crystallinity, the removal of PSS molecules, and moreover a reorientation of the conjugated PEDOT molecules. The latter is reported and quantified here for PEDOT:PSS films for the first time.

In the rapid development of organic electronics, there is a strong need for highly conductive and transparent electrode (TE) materials to act as charge transport layers. In this context, poly(3,4‐ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) is a highly promising candidate, because it can act directly as TE. This makes the use of brittle, rare, and expensive indium tin oxide electrodes dispensable. Modification of the inner film morphology, e.g., by solvent additives can dramatically reduce the sheet resistance of PEDOT:PSS. In this work, it is investigated how the (fluoro)surfactant Zonyl and the co‐solvent ethylene glycol influence the electrical and optical properties of the film, namely, the sheet resistance, the transmission, and the figure of merit for TEs. The electronic characteristics are then related to the morphological changes investigated with grazing incidence small angle X‐ray scattering (GISAXS) and polarized resonant soft X‐ray scattering (P‐SoXS). Using GISAXS, structure evolutions are related to sheet resistances and device characteristics in organic solar cells. Further, the influence of (fluoro)surfactant on the phase separation and relative molecular orientation at polymer interfaces is investigated utilizing P‐SoXS. Transparent PEDOT:PSS films with low sheet resistance are essential for market introduction and mark the next milestone for the success of future organic electronic materials.

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