Publications

@article{Yang2020a,
title = {In Operando GISAXS and GIWAXS Stability Study of Organic Solar Cells Based on PffBT4T-2OD:PC71BM with and without Solvent Additive},
author = {Dan Yang and Franziska C Löhrer and Volker Körstgens and Armin Schreiber and Bing Cao and Sigrid Bernstorff and Peter Müller-Buschbaum},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/advs.202001117},
doi = {https://doi.org/10.1002/advs.202001117},
year = {2020},
date = {2020-01-01},
journal = {Advanced Science},
volume = {7},
number = {16},
pages = {2001117},
abstract = {Abstract Solvent additives are known to modify the morphology of bulk heterojunction active layers to achieve high efficiency organic solar cells. However, the knowledge about the influence of solvent additives on the morphology degradation is limited. Hence, in operando grazing-incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) measurements are applied on a series of PffBT4T-2OD:PC71BM-based solar cells prepared without and with solvent additives. The solar cells fabricated without a solvent additive, with 1,8-diiodoctane (DIO), and with o-chlorobenzaldehyde (CBA) additive show differences in the device degradation and changes in the morphology and crystallinity of the active layers. The mesoscale morphology changes are correlated with the decay of the short-circuit current Jsc and the evolution of crystalline grain sizes is codependent with the decay of open-circuit voltage Voc. Without additive, the loss in Jsc dominates the degradation, whereas with solvent additive (DIO and CBA) the loss in Voc rules the degradation. CBA addition increases the overall device stability as compared to DIO or absence of additive.},
keywords = {crystallinity, degradation, in operando, organic photovoltaics, solvent additives},
pubstate = {published},
tppubtype = {article}
}

@article{Loehrer2020,
title = {Light-Induced and Oxygen-Mediated Degradation Processes in Photoactive Layers Based on PTB7-Th},
author = {Franziska C Löhrer and Christoph Senfter and Christoph J Schaffer and Johannes Schlipf and Daniel Moseguí González and Peng Zhang and Stephan V Roth and Peter Müller-Buschbaum},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adpr.202000047},
doi = {https://doi.org/10.1002/adpr.202000047},
year = {2020},
date = {2020-01-01},
journal = {Advanced Photonics Research},
volume = {1},
number = {1},
pages = {2000047},
abstract = {Low-bandgap polymers are sensitive to various degradation processes, which strongly decrease their lifetime. The chemical and physical changes occurring in the low-bandgap polymer with benzodithiophene units poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and its blend with the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are followed during irradiation-induced aging by combination of various characterization methods. The active layer morphology is investigated using atomic force microscopy (AFM) as well as in-operando grazing incidence small angle X-ray scattering (GISAXS), indicating morphological alterations and material loss due to chemical modifications. Optical spectroscopy gives insights into these chemical processes which lead to significant absorption losses under ambient conditions. Independent of the energy of the absorbed photons, but only in combination with oxygen, the excitation of the polymer leads to a fatal increase in oxidation probability. Fourier transform infrared (FTIR) data highlight the sensitivity of the conjugated polymer backbone to oxidation, a result of lost conjugation and therefore absorption capability. With combined AFM height and infrared (IR) mapping, the chemical degradation and material loss is confirmed on a nanoscale. Although the chemical structure is seriously damaged, the blend morphology is not undergoing major changes.},
keywords = {degradation, Fourier transform infrared, grazing incidence small angle X-ray scattering, low-bandgap polymers, photo-oxidation},
pubstate = {published},
tppubtype = {article}
}