Maciej Kawecki oral presentation (SN2-Tue3-2-2)
Sequential tracking of ionic migration in active electronic devices by means of ToF-SIMS
Empa - Swiss federal laboratories for materials science and technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Electronic devices such as e.g. light-emitting electrochemical cells (LECs), batteries or supercapacitors depend on ionic mobility for their functioning. Approaches allowing direct measurement of voltage and time dependent ionic distributions, however, are highly limited.
LECs  are semi conductive organic light generating devices that consist of a single salt-infused organic layer sandwiched between two electrodes (Figure 1.a). Applying an out-of-plane electric field provokes an ionic redistribution that induces reversible p- and n-doped regions inside the organic layer, separated by an intrinsic region that allows for radiative electron-hole recombination (Figure 1.b) . The association of ionic migration with light emission makes LECs a convenient testing ground for the development of a measurement approach that aims at the tracking of mobile ions in active electronic devices.
Here we use ToF-SIMS sputter profiling to sequentially track the ionic migration inside an active LEC. For this we apply a controlled in-situ electric field and subsequently freeze the active ions in place, immobilizing them inside the solid electrolyte matrix at liquid nitrogen temperature for the measurement duration (Figure 1.c). Throughout the entire measurement duration the electric field between the electrodes is maintained. The distribution of the mobile ions is sequentially captured at chosen times during the migration process and for both field polarities. We present quantitative results visualizing the highly pronounced ionic migration as well as show the time evolution of this migration.
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