Electrical and optical properties of transparent flexible electrodes: Effects of UV ozone and oxygen plasma treatments

Flextrodes are flexible transparent electrodes consisting of ZnO(100 nm)/PEDOT:PSS/silver grid/polyethylene terephthalate (PET) fabricated using a roll-to-roll process. Flextrodes provide a zinc oxide surface on a high-conductivity electrode while maintaining reasonable transparency and good flexibility. They are optimized for use as cathodes (i.e. low work functions) in inverted organic solar cells (OSCs). As-received Flextrode samples have a surface contamination layer that insulates. Prior to use in OSCs, this contamination layer needs to be removed. We tested two surface cleaning methods, i.e., UV-ozone and oxygen plasma, with various treatment times. After cleaning samples were characterized in terms of water contact angle, UV-visible transmittance, and 4-point probe conductivity, using conductive atomic force microscopy, and X-ray/ultraviolet photoelectron spectroscopy. Based on these measurements, we identified optimal conditions and were able to recover work functions of 3.4-3.6 eV without damaging the Flextrodes. (C) 2014 Elsevier B. V. All rights reserved.