Cation Effect of Benzoate Salts on Conductivity Enhancement of PEDOT:PSS and Their Application in Flexible Organic Light-Emitting Diodes

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used flexible electrode material due to its high optical transparency, tunable conductivity, and cost-effective solution processability. However, the excessive insulating PSS content in pristine PEDOT:PSS films leads to an unsatisfactory electrical conductivity and strong acidity. In this work, we introduce a novel class of benzoate salts to significantly enhance the electrical conductivity of PEDOT:PSS by modulating the metal cations. Systematic investigations reveal that the cation species critically influence phase separation and fibrillar morphology evolution in PEDOT:PSS, following the trend K⁺ < Na⁺ < Ag⁺. This behavior is attributed to the synergistic interplay between cation softness parameters and ionic radii, ultimately yielding a remarkable conductivity of 534.18 S/cm for Ag⁺-modified PEDOT:PSS. Leveraging this optimized electrode, we demonstrate high-efficiency flexible organic light-emitting diodes achieving outstanding efficiencies of 75.6 cd/A, 39.6 lm/W, and 22.0%, which stem from the enhanced conductivity and well-matched work function. This finding broadens the variety and scope of additives to enhance the electrical conductivity of PEDOT:PSS and underscores the promising applications of PEDOT:PSS electrodes in high-performance flexible optoelectronic devices.