*2.1. Chemicals*

Polyethylene terephthalate (PET, thickness of 12 μm) foil was obtained from Ecoplast LLC (Khmelnitskiy, Ukraine) and was used as supplied. AT-cut quartz crystals (5 MHz) of a 15 mm diameter were obtained from KVG Quartz Crystal Technology GmbH (Neckarbischofsheim, Germany). Propylene carbonate (PC, 99%), ethanol (technical grade), 3,4 ethylendioxythiophene (EDOT, 97%), and tetrabutylammonium-hexafluorophosphate (TBAPF6, 99.9%) were purchased from Sigma-Aldrich (Taufkirchen, Germany) and were used as supplied.
