Mechanically stable solution-processed transparent conductive electrodes for optoelectronic applications

The bilayer structure of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) coating on silver nanowires (AgNWs) film is a promising structure for replacing indium tin oxide (ITO) as a flexible transparent conductive electrode. Pristine PEDOT:PSS film due to its hydrophilicity and high permeability cannot fully protect AgNWs from mechanical stress and oxidation. Here, we present a composite approach that improves mechanical properties and lifespan of the AgNWs/PEDOT:PSS electrode by adding polyvinyl alcohol (PVA) as a polymer-surfactant. It is shown that addition of PVA improves the conductivity as well as the stability of hybrid electrode under demanding mechanical stress conditions. The drop in conductivity of the hybrid electrode is only 17% after 2000 repeated bending cycles whereas the reference electrode has shown a dramatic drop of 180% in the conductivity. We speculate that generation of hydrogen bonds between PEDOT:PSS and PVA increases adhesivity and cohesivity of the conductive polymer film to the sublayer. So PEDOT:PSS-PVA film not only fixes the arrangement of AgNWs but also improves the welding on cross junction points. By addition of PVA, optoelectronic performance (Figure-of-merit (phi TC)) of the electrode is improved from phi TC = 2.646 x 10-3 ohm-1 for AgNWs/PEDOT:PSS to phi TC = 3.819 x 10-3 ohm-1 for AgNWs/PEDOT:PSS-PVA electrode and power conversion efficiency (PCE) of the polymer solar cell (PSC) is increased by over 17%.