Low-dose (S)TEM elemental analysis of water and oxygen uptake in beam sensitive materials

• Published in: Ultramicroscopy 2020-01, Vol.208, p.112855-112855, Article 112855
• Main Authors: Leijten, Z.J.W.A., Wirix, M.J.M., Strauss, M., Plitzko, J.M., de With, G., Friedrich, H.
• Format: Article
• Language: English
• Subjects: cryo EFTEM; cryo STEM-EELS; Direct electron detector; Electron beam damage; Low-dose; Organic photovoltaics; Oxygen uptake; Water uptake
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2019.112855

•We present low-dose cryo-(S)TEM elemental analysis to assess oxygen- and water-uptake in specific domains in organic photovoltaic donor-acceptor model systems.•Assessing beam damage, i.e., the loss of the oxygen K-edge intensity in EEL spectra, allows a via dose series to define a critical dose below which reliable elemental information can be acquired.•Cryo-STEM-EDX, Cryo-EFTEM and Cryo-STEM-EELS all show that oxygen and water are mainly taken up in the acceptor-rich domains.•Cryo-STEM-EELS can be used to quantify local oxygen concentrations in beam sensitive materials. The performance stability of organic photovoltaics (OPVs) is largely determined by their nanoscale morphology and composition and is highly dependent on the interaction with oxygen and water from air. Low-dose cryo-(S)TEM techniques, in combination with OPV donor-acceptor model systems, can be used to assess oxygen- and water-uptake in the donor, acceptor and their interface. By determining a materials dependent critical electron dose from the decay of the oxygen K-edge intensity in Electron Energy Loss Spectra, we reliably measured oxygen- and water-uptake minimizing and correcting electron beam effects. With measurements below the dose limit the capability of STEM-EDX, EFTEM and STEM-EELS techniques are compared to qualitatively and quantitatively measure oxygen and water uptake in these OPV model systems. Here we demonstrate that oxygen and water is mainly taken up in acceptor-rich regions, and that specific oxygen uptake at the donor-acceptor interphase does not occur. STEM-EELS is shown to be the best suitable technique, enabling quantification of the local oxygen concentration in OPV model systems.