The effect of secondary dopants on screen-printed PEDOT:PSS counter-electrodes for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) gained great attention thanks to high conversion efficiency at ambient indoor light and the possibility of low-cost and eco-friendly fabrication by printing techniques (screen-printing) on different flexible or rigid substrates. These properties predetermine the use of DSSCs in current and future Internet of Things portable and wearable applications. However, one of the main problems of the standard DSSC structure lies in an expensive and unstable Pt counter-electrode (CE) in the liquid electrolyte. Printable conducting polymers, in particular doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) are the promising alternative. This work presents the preparation of the Pt-free counter-electrodes by screen-printing the water-based PEDOT:PSS inks and their optimization by adding secondary dopants, that is, ethylene glycol, polyethylene glycol, and dimethyl sulfoxide. Selected secondary dopants influenced the rheological and structural properties, conductivity, and electrochemical behavior of PEDOT:PSS inks and screen-printed PEDOT:PSS CE. The addition of dopants led to the decreased surface tension of PEDOT:PSS inks, with a subsequent positive effect on better wettability of FTO substrates. The lowest sheet resistance 138 omega/sq, the highest conductivity 91 S/cm, best electrochemical activity towards triiodide reduction and the highest efficiency of DSSCs was evaluated for screen-printed PEDOT:PSS CEs doped with 6 wt% of ethylene glycol.