Crystallization and conformation engineering of solution-processed polymer transparent electrodes with high conductivity

With the cooperative effects of pre-treatment with a polyethylene glycol 4000 (PEG4000) additive and post-treatment with sulfuric acid (H2SO4), the conductivity of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) was improved remarkably. By this method, the pre-treatment PEG4000 additive would form hydrogen bonds with the PSS in PEDOT: PSS, which can effectively reduce the interactions between PEDOT and PSS. Subsequently, the post-treatment H2SO4 could efficiently wash away the intrinsic PSS together with the insulating PEG4000 additive, which not only improved the crystallization but also further optimized the conformation of the PEDOT chains. Meanwhile, the work function of the resulting PEDOT: PSS (S-PEDOT: PSS: PEG4000 (6.5 wt%)) was remarkably reduced and it became more suitable for use as a cathode, compared with pristine PEDOT: PSS. By means of these simple process technologies, a highly conductive and transparent PEDOT: PSS film was achieved. A polymer solar cell device using S-PEDOT: PSS: PEG4000 (6.5 wt%) as the cathode realized a notable power conversion efficiency of 8.1%, which was even superior to an indium tin oxide cathode based device.